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 Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.In the past oysters were raised in much the same way as dirt farmers raised tomatoes - by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other debris, then scattered clean shells about. Next, they "planted" fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat. The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long farmers gathered the baby oysters transplanted them in other waters to speed up their growth, then transplanted them once more into another body of water to fatten them up.Until recently; the supply of wild oysters and those crudely farmed were more than enough to satisfy people's needs. But today the delectable seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.Fortunately, as far back as the early 1900's marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940's a significant breakthrough was made.The marine biologists discovered that by raising the temperature of the water, they could induce oysters to spawn not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat. Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities and temperatures. In addition, the cultivated oysters tasted better. Which of the following best describes the organization of the passage?

Xem chi tiết 1.2 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.In the past oysters were raised in much the same way as dirt farmers raised tomatoes - by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other debris, then scattered clean shells about. Next, they "planted" fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat. The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long farmers gathered the baby oysters transplanted them in other waters to speed up their growth, then transplanted them once more into another body of water to fatten them up.Until recently; the supply of wild oysters and those crudely farmed were more than enough to satisfy people's needs. But today the delectable seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.Fortunately, as far back as the early 1900's marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940's a significant breakthrough was made.The marine biologists discovered that by raising the temperature of the water, they could induce oysters to spawn not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat. Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities and temperatures. In addition, the cultivated oysters tasted better.In what paragraph does the author describe successful methods for increasingthe oyster population?

Xem chi tiết 1.1 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.In the past oysters were raised in much the same way as dirt farmers raised tomatoes - by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other debris, then scattered clean shells about. Next, they "planted" fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat. The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long farmers gathered the baby oysters transplanted them in other waters to speed up their growth, then transplanted them once more into another body of water to fatten them up.Until recently; the supply of wild oysters and those crudely farmed were more than enough to satisfy people's needs. But today the delectable seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.Fortunately, as far back as the early 1900's marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940's a significant breakthrough was made.The marine biologists discovered that by raising the temperature of the water, they could induce oysters to spawn not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat. Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities and temperatures. In addition, the cultivated oysters tasted better.In the passage, the author mentions that the new strains of oyster are ________

Xem chi tiết 3.8 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.In the past oysters were raised in much the same way as dirt farmers raised tomatoes - by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other debris, then scattered clean shells about. Next, they "planted" fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat. The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long farmers gathered the baby oysters transplanted them in other waters to speed up their growth, then transplanted them once more into another body of water to fatten them up.Until recently; the supply of wild oysters and those crudely farmed were more than enough to satisfy people's needs. But today the delectable seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.Fortunately, as far back as the early 1900's marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940's a significant breakthrough was made.The marine biologists discovered that by raising the temperature of the water, they could induce oysters to spawn not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat. Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities and temperatures. In addition, the cultivated oysters tasted better.According to the passage, which of the following words best describes the efforts of the marine biologists working with oysters?

Xem chi tiết 2 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.In the past oysters were raised in much the same way as dirt farmers raised tomatoes - by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other debris, then scattered clean shells about. Next, they "planted" fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat. The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long farmers gathered the baby oysters transplanted them in other waters to speed up their growth, then transplanted them once more into another body of water to fatten them up.Until recently; the supply of wild oysters and those crudely farmed were more than enough to satisfy people's needs. But today the delectable seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.Fortunately, as far back as the early 1900's marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940's a significant breakthrough was made.The marine biologists discovered that by raising the temperature of the water, they could induce oysters to spawn not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat. Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities and temperatures. In addition, the cultivated oysters tasted better.In the passage, which of the following is NOT mentioned as a stage of an oyster's life?

Xem chi tiết 1.2 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.In the past oysters were raised in much the same way as dirt farmers raised tomatoes - by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other debris, then scattered clean shells about. Next, they "planted" fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat. The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long farmers gathered the baby oysters transplanted them in other waters to speed up their growth, then transplanted them once more into another body of water to fatten them up.Until recently; the supply of wild oysters and those crudely farmed were more than enough to satisfy people's needs. But today the delectable seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.Fortunately, as far back as the early 1900's marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940's a significant breakthrough was made.The marine biologists discovered that by raising the temperature of the water, they could induce oysters to spawn not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat. Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities and temperatures. In addition, the cultivated oysters tasted better.In the passage, which of the following is NOT mentioned as a stage of an oyster's life?

Xem chi tiết 1.1 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.In the past oysters were raised in much the same way as dirt farmers raised tomatoes - by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other debris, then scattered clean shells about. Next, they "planted" fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat. The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long farmers gathered the baby oysters transplanted them in other waters to speed up their growth, then transplanted them once more into another body of water to fatten them up.Until recently; the supply of wild oysters and those crudely farmed were more than enough to satisfy people's needs. But today the delectable seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.Fortunately, as far back as the early 1900's marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940's a significant breakthrough was made.The marine biologists discovered that by raising the temperature of the water, they could induce oysters to spawn not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat. Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities and temperatures. In addition, the cultivated oysters tasted better.In the first paragraph, the production of oysters is compared to what other industry?

Xem chi tiết 1.1 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.In the past oysters were raised in much the same way as dirt farmers raised tomatoes - by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other debris, then scattered clean shells about. Next, they "planted" fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat. The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long farmers gathered the baby oysters transplanted them in other waters to speed up their growth, then transplanted them once more into another body of water to fatten them up.Until recently; the supply of wild oysters and those crudely farmed were more than enough to satisfy people's needs. But today the delectable seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.Fortunately, as far back as the early 1900's marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940's a significant breakthrough was made.The marine biologists discovered that by raising the temperature of the water, they could induce oysters to spawn not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat. Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities and temperatures. In addition, the cultivated oysters tasted better.Which of the following would be the best title for the passage?

Xem chi tiết 1 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.The first navigational lights in the New World were probably lanterns hung at harbor entrances. The first lighthouse was put up by the Massachusetts Bay Colony In 1766 on Little Brewster Island at the entrance to Boston Harbor. Paid for and maintained by light dues levied on ships, the original beacon was blown up in 1776. By then there were only a dozen or so true lighthouses in the colonies. Little over a century later, there were 700 lighthouses. The first eight erected on the West Coast in the 1850’s featured the same basic New England design: a Cape Cod dwelling with the tower rising from the center or standing close by. In New England and elsewhere, though, lighthouses reflected a variety of architectural styles. Since most stations in the Northeast were built on rocky eminences, enormous towers were not the rule. Some were made of stone and brick, others of wood or metal. Some stood on pilings or stilts: some were fastened to rock with iron rods. Farther south, from Maryland through the Florida Keys, the coast was low and sandy. It was often necessary to build tall towers there – massive structures like the majestic Cape Hatteras, North Carolina lighthouse, which was lit in 1870. At 190 feet, it is the tallest brick lighthouse in the country. Not withstanding differences in appearance and construction, most American lighthouses shared several features: a light, living quarters, and sometimes a bell (or, later, a foghorn). They also had something else in common: a keeper and, usually, the keeper's family. The keeper's essential task was trimming the lantern Nick in order to maintain a steady bright flame. The earliest keepers came from every walk of life-they were seamen. Farmers, mechanics, rough mill hands-and appointments were often handed out by local customs commissioners as political plums. After the administration of lighthouses was taken over in 1852 by the United States Lighthouse 803rd, an agency of the Treasury Department, the keeper corps gradually became highly professional.Where in the passage does the author tell how lighthouses in the Northeast were fastened to the surrounding rock?

Xem chi tiết 373 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.The first navigational lights in the New World were probably lanterns hung at harbor entrances. The first lighthouse was put up by the Massachusetts Bay Colony In 1766 on Little Brewster Island at the entrance to Boston Harbor. Paid for and maintained by light dues levied on ships, the original beacon was blown up in 1776. By then there were only a dozen or so true lighthouses in the colonies. Little over a century later, there were 700 lighthouses. The first eight erected on the West Coast in the 1850’s featured the same basic New England design: a Cape Cod dwelling with the tower rising from the center or standing close by. In New England and elsewhere, though, lighthouses reflected a variety of architectural styles. Since most stations in the Northeast were built on rocky eminences, enormous towers were not the rule. Some were made of stone and brick, others of wood or metal. Some stood on pilings or stilts: some were fastened to rock with iron rods. Farther south, from Maryland through the Florida Keys, the coast was low and sandy. It was often necessary to build tall towers there – massive structures like the majestic Cape Hatteras, North Carolina lighthouse, which was lit in 1870. At 190 feet, it is the tallest brick lighthouse in the country. Not withstanding differences in appearance and construction, most American lighthouses shared several features: a light, living quarters, and sometimes a bell (or, later, a foghorn). They also had something else in common: a keeper and, usually, the keeper's family. The keeper's essential task was trimming the lantern Nick in order to maintain a steady bright flame. The earliest keepers came from every walk of life-they were seamen. Farmers, mechanics, rough mill hands-and appointments were often handed out by local customs commissioners as political plums. After the administration of lighthouses was taken over in 1852 by the United States Lighthouse 803rd, an agency of the Treasury Department, the keeper corps gradually became highly professional.It can be inferred from the passage that the Treasury Department, after assuming control of the lighthouses, improved which of the following?

Xem chi tiết 703 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.The first navigational lights in the New World were probably lanterns hung at harbor entrances. The first lighthouse was put up by the Massachusetts Bay Colony In 1766 on Little Brewster Island at the entrance to Boston Harbor. Paid for and maintained by light dues levied on ships, the original beacon was blown up in 1776. By then there were only a dozen or so true lighthouses in the colonies. Little over a century later, there were 700 lighthouses. The first eight erected on the West Coast in the 1850’s featured the same basic New England design: a Cape Cod dwelling with the tower rising from the center or standing close by. In New England and elsewhere, though, lighthouses reflected a variety of architectural styles. Since most stations in the Northeast were built on rocky eminences, enormous towers were not the rule. Some were made of stone and brick, others of wood or metal. Some stood on pilings or stilts: some were fastened to rock with iron rods. Farther south, from Maryland through the Florida Keys, the coast was low and sandy. It was often necessary to build tall towers there – massive structures like the majestic Cape Hatteras, North Carolina lighthouse, which was lit in 1870. At 190 feet, it is the tallest brick lighthouse in the country. Not withstanding differences in appearance and construction, most American lighthouses shared several features: a light, living quarters, and sometimes a bell (or, later, a foghorn). They also had something else in common: a keeper and, usually, the keeper's family. The keeper's essential task was trimming the lantern Nick in order to maintain a steady bright flame. The earliest keepers came from every walk of life-they were seamen. Farmers, mechanics, rough mill hands-and appointments were often handed out by local customs commissioners as political plums. After the administration of lighthouses was taken over in 1852 by the United States Lighthouse 803rd, an agency of the Treasury Department, the keeper corps gradually became highly professional.In line 15, to which of the following does the word "They" refer?

Xem chi tiết 575 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.The first navigational lights in the New World were probably lanterns hung at harbor entrances. The first lighthouse was put up by the Massachusetts Bay Colony In 1766 on Little Brewster Island at the entrance to Boston Harbor. Paid for and maintained by light dues levied on ships, the original beacon was blown up in 1776. By then there were only a dozen or so true lighthouses in the colonies. Little over a century later, there were 700 lighthouses. The first eight erected on the West Coast in the 1850’s featured the same basic New England design: a Cape Cod dwelling with the tower rising from the center or standing close by. In New England and elsewhere, though, lighthouses reflected a variety of architectural styles. Since most stations in the Northeast were built on rocky eminences, enormous towers were not the rule. Some were made of stone and brick, others of wood or metal. Some stood on pilings or stilts: some were fastened to rock with iron rods. Farther south, from Maryland through the Florida Keys, the coast was low and sandy. It was often necessary to build tall towers there – massive structures like the majestic Cape Hatteras, North Carolina lighthouse, which was lit in 1870. At 190 feet, it is the tallest brick lighthouse in the country. Not withstanding differences in appearance and construction, most American lighthouses shared several features: a light, living quarters, and sometimes a bell (or, later, a foghorn). They also had something else in common: a keeper and, usually, the keeper's family. The keeper's essential task was trimming the lantern Nick in order to maintain a steady bright flame. The earliest keepers came from every walk of life-they were seamen. Farmers, mechanics, rough mill hands-and appointments were often handed out by local customs commissioners as political plums. After the administration of lighthouses was taken over in 1852 by the United States Lighthouse 803rd, an agency of the Treasury Department, the keeper corps gradually became highly professional.According to the passage, where can the tallest brick lighthouse in the United States be found?

Xem chi tiết 471 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.The first navigational lights in the New World were probably lanterns hung at harbor entrances. The first lighthouse was put up by the Massachusetts Bay Colony In 1766 on Little Brewster Island at the entrance to Boston Harbor. Paid for and maintained by light dues levied on ships, the original beacon was blown up in 1776. By then there were only a dozen or so true lighthouses in the colonies. Little over a century later, there were 700 lighthouses. The first eight erected on the West Coast in the 1850’s featured the same basic New England design: a Cape Cod dwelling with the tower rising from the center or standing close by. In New England and elsewhere, though, lighthouses reflected a variety of architectural styles. Since most stations in the Northeast were built on rocky eminences, enormous towers were not the rule. Some were made of stone and brick, others of wood or metal. Some stood on pilings or stilts: some were fastened to rock with iron rods. Farther south, from Maryland through the Florida Keys, the coast was low and sandy. It was often necessary to build tall towers there – massive structures like the majestic Cape Hatteras, North Carolina lighthouse, which was lit in 1870. At 190 feet, it is the tallest brick lighthouse in the country. Not withstanding differences in appearance and construction, most American lighthouses shared several features: a light, living quarters, and sometimes a bell (or, later, a foghorn). They also had something else in common: a keeper and, usually, the keeper's family. The keeper's essential task was trimming the lantern Nick in order to maintain a steady bright flame. The earliest keepers came from every walk of life-they were seamen. Farmers, mechanics, rough mill hands-and appointments were often handed out by local customs commissioners as political plums. After the administration of lighthouses was taken over in 1852 by the United States Lighthouse 803rd, an agency of the Treasury Department, the keeper corps gradually became highly professional.It can be inferred from the passage that lighthouses in the Northeast did not need high towers because ________ .

Xem chi tiết 698 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.The first navigational lights in the New World were probably lanterns hung at harbor entrances. The first lighthouse was put up by the Massachusetts Bay Colony In 1766 on Little Brewster Island at the entrance to Boston Harbor. Paid for and maintained by light dues levied on ships, the original beacon was blown up in 1776. By then there were only a dozen or so true lighthouses in the colonies. Little over a century later, there were 700 lighthouses. The first eight erected on the West Coast in the 1850’s featured the same basic New England design: a Cape Cod dwelling with the tower rising from the center or standing close by. In New England and elsewhere, though, lighthouses reflected a variety of architectural styles. Since most stations in the Northeast were built on rocky eminences, enormous towers were not the rule. Some were made of stone and brick, others of wood or metal. Some stood on pilings or stilts: some were fastened to rock with iron rods. Farther south, from Maryland through the Florida Keys, the coast was low and sandy. It was often necessary to build tall towers there – massive structures like the majestic Cape Hatteras, North Carolina lighthouse, which was lit in 1870. At 190 feet, it is the tallest brick lighthouse in the country. Not withstanding differences in appearance and construction, most American lighthouses shared several features: a light, living quarters, and sometimes a bell (or, later, a foghorn). They also had something else in common: a keeper and, usually, the keeper's family. The keeper's essential task was trimming the lantern Nick in order to maintain a steady bright flame. The earliest keepers came from every walk of life-they were seamen. Farmers, mechanics, rough mill hands-and appointments were often handed out by local customs commissioners as political plums. After the administration of lighthouses was taken over in 1852 by the United States Lighthouse 803rd, an agency of the Treasury Department, the keeper corps gradually became highly professional.Why does the author mention the Massachusetts Bay Colony?

Xem chi tiết 2.3 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.The first navigational lights in the New World were probably lanterns hung at harbor entrances. The first lighthouse was put up by the Massachusetts Bay Colony In 1766 on Little Brewster Island at the entrance to Boston Harbor. Paid for and maintained by light dues levied on ships, the original beacon was blown up in 1776. By then there were only a dozen or so true lighthouses in the colonies. Little over a century later, there were 700 lighthouses. The first eight erected on the West Coast in the 1850’s featured the same basic New England design: a Cape Cod dwelling with the tower rising from the center or standing close by. In New England and elsewhere, though, lighthouses reflected a variety of architectural styles. Since most stations in the Northeast were built on rocky eminences, enormous towers were not the rule. Some were made of stone and brick, others of wood or metal. Some stood on pilings or stilts: some were fastened to rock with iron rods. Farther south, from Maryland through the Florida Keys, the coast was low and sandy. It was often necessary to build tall towers there – massive structures like the majestic Cape Hatteras, North Carolina lighthouse, which was lit in 1870. At 190 feet, it is the tallest brick lighthouse in the country. Not withstanding differences in appearance and construction, most American lighthouses shared several features: a light, living quarters, and sometimes a bell (or, later, a foghorn). They also had something else in common: a keeper and, usually, the keeper's family. The keeper's essential task was trimming the lantern Nick in order to maintain a steady bright flame. The earliest keepers came from every walk of life-they were seamen. Farmers, mechanics, rough mill hands-and appointments were often handed out by local customs commissioners as political plums. After the administration of lighthouses was taken over in 1852 by the United States Lighthouse 803rd, an agency of the Treasury Department, the keeper corps gradually became highly professional.What is the best title for the passage?

Xem chi tiết 415 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.One of the most important (31) ________ of a standardized test is time. You’ll only be allowed a certain number of minutes for each section, so it is very essential that you use your time wisely. The most significant time strategy is pacing yourself. Before you initiate, take just a few seconds to review the test, noting the number of questions and the sections that looks easier than the rest. Then, make a rough time plan based (32) ________ the amount of time  available to you. Mark the halfway point on your test and make a memo beside that mark of the time when the testing period is half over.Once you start the test, continue moving. If you work slowly in an attempt to make  fewer mistakes, your mind will become bored and begin to wander. You’ll end up with far (33) ________  mistakes if you’re not concentrating. If you take too long to answer questions that stump you, you may end up running out of time before you finish. So don’t stop for difficult questions. Skip them and move on. You can come back to them later if you have time. A question that takes you five seconds to answer counts as much as one that takes you several minutes, so pick up the easy points first. (34) ________, answering the easier questions first helps build your confidence and gets you in the testing groove. If you’re a little ahead, you know you’re on track and may even have a little time left to check your work. If you’re a little behind, you have several choices. You can pick up the pace a little, but do this only if you can do it (35) ________.Điền câu 35

Xem chi tiết 384 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.One of the most important (31) ________ of a standardized test is time. You’ll only be allowed a certain number of minutes for each section, so it is very essential that you use your time wisely. The most significant time strategy is pacing yourself. Before you initiate, take just a few seconds to review the test, noting the number of questions and the sections that looks easier than the rest. Then, make a rough time plan based (32) ________ the amount of time  available to you. Mark the halfway point on your test and make a memo beside that mark of the time when the testing period is half over.Once you start the test, continue moving. If you work slowly in an attempt to make  fewer mistakes, your mind will become bored and begin to wander. You’ll end up with far (33) ________  mistakes if you’re not concentrating. If you take too long to answer questions that stump you, you may end up running out of time before you finish. So don’t stop for difficult questions. Skip them and move on. You can come back to them later if you have time. A question that takes you five seconds to answer counts as much as one that takes you several minutes, so pick up the easy points first. (34) ________, answering the easier questions first helps build your confidence and gets you in the testing groove. If you’re a little ahead, you know you’re on track and may even have a little time left to check your work. If you’re a little behind, you have several choices. You can pick up the pace a little, but do this only if you can do it (35) ________.Điền câu 34

Xem chi tiết 367 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.One of the most important (31) ________ of a standardized test is time. You’ll only be allowed a certain number of minutes for each section, so it is very essential that you use your time wisely. The most significant time strategy is pacing yourself. Before you initiate, take just a few seconds to review the test, noting the number of questions and the sections that looks easier than the rest. Then, make a rough time plan based (32) ________ the amount of time  available to you. Mark the halfway point on your test and make a memo beside that mark of the time when the testing period is half over.Once you start the test, continue moving. If you work slowly in an attempt to make  fewer mistakes, your mind will become bored and begin to wander. You’ll end up with far (33) ________  mistakes if you’re not concentrating. If you take too long to answer questions that stump you, you may end up running out of time before you finish. So don’t stop for difficult questions. Skip them and move on. You can come back to them later if you have time. A question that takes you five seconds to answer counts as much as one that takes you several minutes, so pick up the easy points first. (34) ________, answering the easier questions first helps build your confidence and gets you in the testing groove. If you’re a little ahead, you know you’re on track and may even have a little time left to check your work. If you’re a little behind, you have several choices. You can pick up the pace a little, but do this only if you can do it (35) ________.Điền câu 33

Xem chi tiết 294 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.One of the most important (31) ________ of a standardized test is time. You’ll only be allowed a certain number of minutes for each section, so it is very essential that you use your time wisely. The most significant time strategy is pacing yourself. Before you initiate, take just a few seconds to review the test, noting the number of questions and the sections that looks easier than the rest. Then, make a rough time plan based (32) ________ the amount of time  available to you. Mark the halfway point on your test and make a memo beside that mark of the time when the testing period is half over.Once you start the test, continue moving. If you work slowly in an attempt to make  fewer mistakes, your mind will become bored and begin to wander. You’ll end up with far (33) ________  mistakes if you’re not concentrating. If you take too long to answer questions that stump you, you may end up running out of time before you finish. So don’t stop for difficult questions. Skip them and move on. You can come back to them later if you have time. A question that takes you five seconds to answer counts as much as one that takes you several minutes, so pick up the easy points first. (34) ________, answering the easier questions first helps build your confidence and gets you in the testing groove. If you’re a little ahead, you know you’re on track and may even have a little time left to check your work. If you’re a little behind, you have several choices. You can pick up the pace a little, but do this only if you can do it (35) ________.Điền câu 32

Xem chi tiết 272 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, c, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.One of the most important (31) ________ of a standardized test is time. You’ll only be allowed a certain number of minutes for each section, so it is very essential that you use your time wisely. The most significant time strategy is pacing yourself. Before you initiate, take just a few seconds to review the test, noting the number of questions and the sections that looks easier than the rest. Then, make a rough time plan based (32) ________ the amount of time  available to you. Mark the halfway point on your test and make a memo beside that mark of the time when the testing period is half over.Once you start the test, continue moving. If you work slowly in an attempt to make  fewer mistakes, your mind will become bored and begin to wander. You’ll end up with far (33) ________  mistakes if you’re not concentrating. If you take too long to answer questions that stump you, you may end up running out of time before you finish. So don’t stop for difficult questions. Skip them and move on. You can come back to them later if you have time. A question that takes you five seconds to answer counts as much as one that takes you several minutes, so pick up the easy points first. (34) ________, answering the easier questions first helps build your confidence and gets you in the testing groove. If you’re a little ahead, you know you’re on track and may even have a little time left to check your work. If you’re a little behind, you have several choices. You can pick up the pace a little, but do this only if you can do it (35) ________.Điền câu 31

Xem chi tiết 420 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questionsProtons and neutrons have nearly equal mass and size, but protons carry a positive electrical charge, while neutrons carry no charge at all. Protons and neutrons are bound together by the strong nuclear force, one of the four basic forces in the universe. Protons and neutrons give atoms some of their most basic properties. Elements are defined by two numbers: their atomic number, which is equal to the number of protons they have, and their atomic weight, which is equal to total number of their neutrons and protons. In most lighter atoms, the number of neutrons and protons is equal, and the element is stable. In heavier atoms, however, there are more neutrons than protons, and the element is unstable, eventually losing neutrons through radioactive decay until a neutral state is reached. Electrons are negatively charged particles. They are bound to their atoms through electromagnetic attraction. Opposite electrical charges attract one another, so the positive charge of the proton helps to keep the negatively charged electron in orbit around the nucleus of the atom. Electrons are different from neutrons in that they cannot be broken down into smaller particles. They are also far smaller and lighter than neutrons and protons. An electron is about one thousandth of the diameter of a proton and an even smaller fraction of its mass. Electrons circle the protons and neutrons at the center of the atom in orbits. These orbits are often called electron shells. The closer the orbit is to the center of the atom, the lower its energy is. There are seven electron shells, and each higher level can hold more electrons than the previous shell. Electrons naturally seek to occupy the lowest shell possible. So, if there is space in a lower shell, an electron will drop down to occupy that space. At temperatures higher than a few hundred degrees, electrons will gain energy and move to a higher shell, but only momentarily. When the electrons drop back down to their natural shell, they emit light. This is why fires and other very hot objects seem to glow. Electrons are also primarily responsible for many of the chemical properties of atoms. Since electrons seek to occupy the lowest electron shell possible, they will move from one atom to another if there is a space available in a lower electron shell. For example, if there is an atom with an open space in its third shell, and it comes into contact with an atom with electrons in its fourth shell, the first atom will take one of these electrons to complete its third shell. When this happens, the two atoms will be chemically bonded to form a molecule. Furthermore, atoms sometimes lose electrons in collisions with other atoms. When this happens, the radio of protons and electrons in the atom changes, and therefore, the overall electrical charge of the atom changes as well. These atoms are called isotopes, and they have significantly different chemical properties from their parent atomsAccording to paragraph 4, which property of electrons is responsible for chemical bonding? 

Xem chi tiết 356 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.Protons and neutrons have nearly equal mass and size, but protons carry a positive electrical charge, while neutrons carry no charge at all. Protons and neutrons are bound together by the strong nuclear force, one of the four basic forces in the universe. Protons and neutrons give atoms some of their most basic properties. Elements are defined by two numbers: their atomic number, which is equal to the number of protons they have, and their atomic weight, which is equal to total number of their neutrons and protons. In most lighter atoms, the number of neutrons and protons is equal, and the element is stable. In heavier atoms, however, there are more neutrons than protons, and the element is unstable, eventually losing neutrons through radioactive decay until a neutral state is reached. Electrons are negatively charged particles. They are bound to their atoms through electromagnetic attraction. Opposite electrical charges attract one another, so the positive charge of the proton helps to keep the negatively charged electron in orbit around the nucleus of the atom. Electrons are different from neutrons in that they cannot be broken down into smaller particles. They are also far smaller and lighter than neutrons and protons. An electron is about one thousandth of the diameter of a proton and an even smaller fraction of its mass. Electrons circle the protons and neutrons at the center of the atom in orbits. These orbits are often called electron shells. The closer the orbit is to the center of the atom, the lower its energy is. There are seven electron shells, and each higher level can hold more electrons than the previous shell. Electrons naturally seek to occupy the lowest shell possible. So, if there is space in a lower shell, an electron will drop down to occupy that space. At temperatures higher than a few hundred degrees, electrons will gain energy and move to a higher shell, but only momentarily. When the electrons drop back down to their natural shell, they emit light. This is why fires and other very hot objects seem to glow. Electrons are also primarily responsible for many of the chemical properties of atoms. Since electrons seek to occupy the lowest electron shell possible, they will move from one atom to another if there is a space available in a lower electron shell. For example, if there is an atom with an open space in its third shell, and it comes into contact with an atom with electrons in its fourth shell, the first atom will take one of these electrons to complete its third shell. When this happens, the two atoms will be chemically bonded to form a molecule. Furthermore, atoms sometimes lose electrons in collisions with other atoms. When this happens, the radio of protons and electrons in the atom changes, and therefore, the overall electrical charge of the atom changes as well. These atoms are called isotopes, and they have significantly different chemical properties from their parent atomsAccording to the passage, all of the following are true of electrons EXCEPT __________. 

Xem chi tiết 424 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.Atomic were once thought to be fundamental pieces of matter, but they are in turn made of smaller subatomic particles There are three major subatomic particles neutrons, protons, and electronic. Protons and neutrons can be broken into even smaller units, but these smaller units not occur naturally in nature and are thought to only be produced in manmade particle accelerators and perhaps in extreme stellar events like supernovas. The structure of an atom can best be described as a small solar system, with the neutrons at the center and the electrons circling them in various orbits, just as the planets circle the sun. In reality, the structure of an atom is far more complex, because the laws of physics are fundamentally different at the atomic level than at the level of the observable word. The true nature of atomic structure can only be expressed accurately through complex mathematical formulas. This explanation, however, is of little use to most average people.Protons and neutrons have nearly equal mass and size, but protons carry a positive electrical charge, while neutrons carry no charge at all. Protons and neutrons are bound together by the strong nuclear force, one of the four basic forces in the universe. Protons and neutrons give atoms some of their most basic properties. Elements are defined by two numbers: their atomic number, which is equal to the number of protons they have, and their atomic weight, which is equal to total number of their neutrons and protons. In most lighter atoms, the number of neutrons and protons is equal, and the element is stable. In heavier atoms, however, there are more neutrons than protons, and the element is unstable, eventually losing neutrons through radioactive decay until a neutral state is reached.Electrons are negatively charged particles. They are bound to their atoms through electromagnetic attraction. Opposite electrical charges attract one another, so the positive charge of the proton helps to keep the negatively charged electron in orbit around the nucleus of the atom. Electrons are different from neutrons in that they cannot be broken down into smaller particles. They are also far smaller and lighter than neutrons and protons. An electron is about one thousandth of the diameter of a proton and an even smaller fraction of its mass. Electrons circle the protons and neutrons at the center of the atom in orbits. These orbits are often called electron shells. The closer the orbit is to the center of the atom, the lower its energy is. There are seven electron shells, and each higher level can hold more electrons than the previous shell. Electrons naturally seek to occupy the lowest shell possible. So, if there is space in a lower shell, an electron will drop down to occupy that space. At temperatures higher than a few hundred degrees, electrons will gain energy and move to a higher shell, but only momentarily. When the electrons drop back down to their natural shell, they emit light. This is why fires and other very hot objects seem to glow.According to paragraph 3, when does an atom produce light?

Xem chi tiết 397 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions. Atomic were once thought to be fundamental pieces of matter, but they are in turn made of smaller subatomic particles There are three major subatomic particles neutrons, protons, and electronic. Protons and neutrons can be broken into even smaller units, but these smaller units not occur naturally in nature and are thought to only be produced in manmade particle accelerators and perhaps in extreme stellar events like supernovas. The structure of an atom can best be described as a small solar system, with the neutrons at the center and the electrons circling them in various orbits, just as the planets circle the sun. In reality, the structure of an atom is far more complex, because the laws of physics are fundamentally different at the atomic level than at the level of the observable word. The true nature of atomic structure can only be expressed accurately through complex mathematical formulas. This explanation, however, is of little use to most average people. Protons and neutrons have nearly equal mass and size, but protons carry a positive electrical charge, while neutrons carry no charge at all. Protons and neutrons are bound together by the strong nuclear force, one of the four basic forces in the universe. Protons and neutrons give atoms some of their most basic properties. Elements are defined by two numbers: their atomic number, which is equal to the number of protons they have, and their atomic weight, which is equal to total number of their neutrons and protons. In most lighter atoms, the number of neutrons and protons is equal, and the element is stable. In heavier atoms, however, there are more neutrons than protons, and the element is unstable, eventually losing neutrons through radioactive decay until a neutral state is reached. Electrons are negatively charged particles. They are bound to their atoms through electromagnetic attraction. Opposite electrical charges attract one another, so the positive charge of the proton helps to keep the negatively charged electron in orbit around the nucleus of the atom. Electrons are different from neutrons in that they cannot be broken down into smaller particles. They are also far smaller and lighter than neutrons and protons. An electron is about one thousandth of the diameter of a proton and an even smaller fraction of its mass. Electrons circle the protons and neutrons at the center of the atom in orbits. These orbits are often called electron shells. The closer the orbit is to the center of the atom, the lower its energy is. There are seven electron shells, and each higher level can hold more electrons than the previous shell. Electrons naturally seek to occupy the lowest shell possible. So, if there is space in a lower shell, an electron will drop down to occupy that space. At temperatures higher than a few hundred degrees, electrons will gain energy and move to a higher shell, but only momentarily. When the electrons drop back down to their natural shell, they emit light. This is why fires and other very hot objects seem to glow.The phrase "one another" in bold in paragraph 3 refers to _______. 

Xem chi tiết 318 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questionsAtomic were once thought to be fundamental pieces of matter, but they are in turn made of smaller subatomic particles There are three major subatomic particles neutrons, protons, and electronic. Protons and neutrons can be broken into even smaller units, but these smaller units not occur naturally in nature and are thought to only be produced in manmade particle accelerators and perhaps in extreme stellar events like supernovas. The structure of an atom can best be described as a small solar system, with the neutrons at the center and the electrons circling them in various orbits, just as the planets circle the sun. In reality, the structure of an atom is far more complex, because the laws of physics are fundamentally different at the atomic level than at the level of the observable word. The true nature of atomic structure can only be expressed accurately through complex mathematical formulas. This explanation, however, is of little use to most average people. Protons and neutrons have nearly equal mass and size, but protons carry a positive electrical charge, while neutrons carry no charge at all. Protons and neutrons are bound together by the strong nuclear force, one of the four basic forces in the universe. Protons and neutrons give atoms some of their most basic properties. Elements are defined by two numbers: their atomic number, which is equal to the number of protons they have, and their atomic weight, which is equal to total number of their neutrons and protons. In most lighter atoms, the number of neutrons and protons is equal, and the element is stable. In heavier atoms, however, there are more neutrons than protons, and the element is unstable, eventually losing neutrons through radioactive decay until a neutral state is reached. Electrons are negatively charged particles. They are bound to their atoms through electromagnetic attraction. Opposite electrical charges attract one another, so the positive charge of the proton helps to keep the negatively charged electron in orbit around the nucleus of the atom. Electrons are different from neutrons in that they cannot be broken down into smaller particles. They are also far smaller and lighter than neutrons and protons. An electron is about one thousandth of the diameter of a proton and an even smaller fraction of its mass. Electrons circle the protons and neutrons at the center of the atom in orbits. These orbits are often called electron shells. The closer the orbit is to the center of the atom, the lower its energy is. There are seven electron shells, and each higher level can hold more electrons than the previous shell. Electrons naturally seek to occupy the lowest shell possible. So, if there is space in a lower shell, an electron will drop down to occupy that space. At temperatures higher than a few hundred degrees, electrons will gain energy and move to a higher shell, but only momentarily. When the electrons drop back down to their natural shell, they emit light. This is why fires and other very hot objects seem to glowAccording to the information in paragraph 2, what will happen if an atom has more neutrons than protons? 

Xem chi tiết 387 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions. Atomic were once thought to be fundamental pieces of matter, but they are in turn made of smaller subatomic particles There are three major subatomic particles neutrons, protons, and electronic. Protons and neutrons can be broken into even smaller units, but these smaller units not occur naturally in nature and are thought to only be produced in manmade particle accelerators and perhaps in extreme stellar events like supernovas. The structure of an atom can best be described as a small solar system, with the neutrons at the center and the electrons circling them in various orbits, just as the planets circle the sun. In reality, the structure of an atom is far more complex, because the laws of physics are fundamentally different at the atomic level than at the level of the observable word. The true nature of atomic structure can only be expressed accurately through complex mathematical formulas. This explanation, however, is of little use to most average people. Protons and neutrons have nearly equal mass and size, but protons carry a positive electrical charge, while neutrons carry no charge at all. Protons and neutrons are bound together by the strong nuclear force, one of the four basic forces in the universe. Protons and neutrons give atoms some of their most basic properties. Elements are defined by two numbers: their atomic number, which is equal to the number of protons they have, and their atomic weight, which is equal to total number of their neutrons and protons. In most lighter atoms, the number of neutrons and protons is equal, and the element is stable. In heavier atoms, however, there are more neutrons than protons, and the element is unstable, eventually losing neutrons through radioactive decay until a neutral state is reachedThe word "stable" in bold in paragraph 2 is closest in meaning to _____. 

Xem chi tiết 0.9 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions. Atomic were once thought to be fundamental pieces of matter, but they are in turn made of smaller subatomic particles There are three major subatomic particles neutrons, protons, and electronic. Protons and neutrons can be broken into even smaller units, but these smaller units not occur naturally in nature and are thought to only be produced in manmade particle accelerators and perhaps in extreme stellar events like supernovas. The structure of an atom can best be described as a small solar system, with the neutrons at the center and the electrons circling them in various orbits, just as the planets circle the sun. In reality, the structure of an atom is far more complex, because the laws of physics are fundamentally different at the atomic level than at the level of the observable word. The true nature of atomic structure can only be expressed accurately through complex mathematical formulas. This explanation, however, is of little use to most average people. Protons and neutrons have nearly equal mass and size, but protons carry a positive electrical charge, while neutrons carry no charge at all. Protons and neutrons are bound together by the strong nuclear force, one of the four basic forces in the universe. Protons and neutrons give atoms some of their most basic properties. Elements are defined by two numbers: their atomic number, which is equal to the number of protons they have, and their atomic weight, which is equal to total number of their neutrons and protons. In most lighter atoms, the number of neutrons and protons is equal, and the element is stable. In heavier atoms, however, there are more neutrons than protons, and the element is unstable, eventually losing neutrons through radioactive decay until a neutral state is reached.According to paragraph 2, an atom's atomic number is determined by __________. 

Xem chi tiết 418 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions. Atomic were once thought to be fundamental pieces of matter, but they are in turn made of smaller subatomic particles There are three major subatomic particles neutrons, protons, and electronic. Protons and neutrons can be broken into even smaller units, but these smaller units not occur naturally in nature and are thought to only be produced in manmade particle accelerators and perhaps in extreme stellar events like supernovas. The structure of an atom can best be described as a small solar system, with the neutrons at the center and the electrons circling them in various orbits, just as the planets circle the sun. In reality, the structure of an atom is far more complex, because the laws of physics are fundamentally different at the atomic level than at the level of the observable word. The true nature of atomic structure can only be expressed accurately through complex mathematical formulas. This explanation, however, is of little use to most average people. Protons and neutrons have nearly equal mass and size, but protons carry a positive electrical charge, while neutrons carry no charge at all. Protons and neutrons are bound together by the strong nuclear force, one of the four basic forces in the universe. Protons and neutrons give atoms some of their most basic properties. Elements are defined by two numbers: their atomic number, which is equal to the number of protons they have, and their atomic weight, which is equal to total number of their neutrons and protons. In most lighter atoms, the number of neutrons and protons is equal, and the element is stable. In heavier atoms, however, there are more neutrons than protons, and the element is unstable, eventually losing neutrons through radioactive decay until a neutral state is reached. In paragraph 1, why does the author compare the structure of an atom to a solar system?

Xem chi tiết 304 lượt xem 5 năm trước