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Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 36 to 42.Life originated in the early seas less than a billion years after the Earth was formed. Yet another three billions years were to pass before the first plants and animals appeared on the continents. Life's transition from the sea to the land was perhaps as much of an evolutionary challenge as was the genesis of life.What forms of life were able to make such a drastic change in lifestyle? The traditional view of the first terrestrial organisms is based on megafossils - relatively large specimens of essential whole plants and animals. Vascular plants, related to modern seed plants and ferns, left the first comprehensive megafossil record. Because of this, it has been commonly assumed that the sequence of terrestrialization reflected the evolution of 10 modern terrestrial ecosystems. In this view, primitive vascular plants first colonized the margins of continental waters, followed by animals that fed on the plants, and lastly by the animals that preyed on the plant-eaters. Moreover, the megafossils suggest that terrestrial life appeared and diversified explosively near the boundary between the Silurian and the Devonian periods, a little more than 400 million years ago.Recently, however, paleontologists have been taking a closer look at sediments below this Silurian- Devonian geological boundary. It turns out that some fossils can be extracted from these sediments by putting the rock in an acid bath. The technique has uncovered new evidence from sediments that were deposited near the shores of the ancient oceans - plant microfossils and microscopic pieces of small animals. In many instances, the specimens are less than one-tenth of a millimeter in diameter. Although they were entombed in the rocks for hundreds of millions of years, many of the fossils consist of the organic remains of the organism.These discovered fossils have not only revealed the existence ofpreviously unknown organisms, but have also pushed back these dates for the invasion of land by multicellular organisms. Our view about the nature of the early plants and animal communities are now being revised. And with those revisions come new speculations about the first terrestrial life-formsThe word "they" refers to ______.

Xem chi tiết 321 lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 36 to 42.Life originated in the early seas less than a billion years after the Earth was formed. Yet another three billions years were to pass before the first plants and animals appeared on the continents. Life's transition from the sea to the land was perhaps as much of an evolutionary challenge as was the genesis of life.What forms of life were able to make such a drastic change in lifestyle? The traditional view of the first terrestrial organisms is based on megafossils - relatively large specimens of essential whole plants and animals. Vascular plants, related to modern seed plants and ferns, left the first comprehensive megafossil record. Because of this, it has been commonly assumed that the sequence of terrestrialization reflected the evolution of 10 modern terrestrial ecosystems. In this view, primitive vascular plants first colonized the margins of continental waters, followed by animals that fed on the plants, and lastly by the animals that preyed on the plant-eaters. Moreover, the megafossils suggest that terrestrial life appeared and diversified explosively near the boundary between the Silurian and the Devonian periods, a little more than 400 million years ago.Recently, however, paleontologists have been taking a closer look at sediments below this Silurian- Devonian geological boundary. It turns out that some fossils can be extracted from these sediments by putting the rock in an acid bath. The technique has uncovered new evidence from sediments that were deposited near the shores of the ancient oceans - plant microfossils and microscopic pieces of small animals. In many instances, the specimens are less than one-tenth of a millimeter in diameter. Although they were entombed in the rocks for hundreds of millions of years, many of the fossils consist of the organic remains of the organism.These discovered fossils have not only revealed the existence ofpreviously unknown organisms, but have also pushed back these dates for the invasion of land by multicellular organisms. Our view about the nature of the early plants and animal communities are now being revised. And with those revisions come new speculations about the first terrestrial life-formsThe word "extracted" is closest in meaning to ___________.

Xem chi tiết 668 lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 36 to 42.Life originated in the early seas less than a billion years after the Earth was formed. Yet another three billions years were to pass before the first plants and animals appeared on the continents. Life's transition from the sea to the land was perhaps as much of an evolutionary challenge as was the genesis of life.What forms of life were able to make such a drastic change in lifestyle? The traditional view of the first terrestrial organisms is based on megafossils - relatively large specimens of essential whole plants and animals. Vascular plants, related to modern seed plants and ferns, left the first comprehensive megafossil record. Because of this, it has been commonly assumed that the sequence of terrestrialization reflected the evolution of 10 modern terrestrial ecosystems. In this view, primitive vascular plants first colonized the margins of continental waters, followed by animals that fed on the plants, and lastly by the animals that preyed on the plant-eaters. Moreover, the megafossils suggest that terrestrial life appeared and diversified explosively near the boundary between the Silurian and the Devonian periods, a little more than 400 million years ago.Recently, however, paleontologists have been taking a closer look at sediments below this Silurian- Devonian geological boundary. It turns out that some fossils can be extracted from these sediments by putting the rock in an acid bath. The technique has uncovered new evidence from sediments that were deposited near the shores of the ancient oceans - plant microfossils and microscopic pieces of small animals. In many instances, the specimens are less than one-tenth of a millimeter in diameter. Although they were entombed in the rocks for hundreds of millions of years, many of the fossils consist of the organic remains of the organism.These discovered fossils have not only revealed the existence ofpreviously unknown organisms, but have also pushed back these dates for the invasion of land by multicellular organisms. Our view about the nature of the early plants and animal communities are now being revised. And with those revisions come new speculations about the first terrestrial life-formsAccording to the passage, what happened about 400 million years ago?

Xem chi tiết 431 lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 36 to 42.Life originated in the early seas less than a billion years after the Earth was formed. Yet another three billions years were to pass before the first plants and animals appeared on the continents. Life's transition from the sea to the land was perhaps as much of an evolutionary challenge as was the genesis of life.What forms of life were able to make such a drastic change in lifestyle? The traditional view of the first terrestrial organisms is based on megafossils - relatively large specimens of essential whole plants and animals. Vascular plants, related to modern seed plants and ferns, left the first comprehensive megafossil record. Because of this, it has been commonly assumed that the sequence of terrestrialization reflected the evolution of 10 modern terrestrial ecosystems. In this view, primitive vascular plants first colonized the margins of continental waters, followed by animals that fed on the plants, and lastly by the animals that preyed on the plant-eaters. Moreover, the megafossils suggest that terrestrial life appeared and diversified explosively near the boundary between the Silurian and the Devonian periods, a little more than 400 million years ago.Recently, however, paleontologists have been taking a closer look at sediments below this Silurian- Devonian geological boundary. It turns out that some fossils can be extracted from these sediments by putting the rock in an acid bath. The technique has uncovered new evidence from sediments that were deposited near the shores of the ancient oceans - plant microfossils and microscopic pieces of small animals. In many instances, the specimens are less than one-tenth of a millimeter in diameter. Although they were entombed in the rocks for hundreds of millions of years, many of the fossils consist of the organic remains of the organism.These discovered fossils have not only revealed the existence ofpreviously unknown organisms, but have also pushed back these dates for the invasion of land by multicellular organisms. Our view about the nature of the early plants and animal communities are now being revised. And with those revisions come new speculations about the first terrestrial life-formsAccording to the theory that the author calls "the traditional view", what was the first form of life to appear on land?

Xem chi tiết 1.8 K lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 36 to 42.Life originated in the early seas less than a billion years after the Earth was formed. Yet another three billions years were to pass before the first plants and animals appeared on the continents. Life's transition from the sea to the land was perhaps as much of an evolutionary challenge as was the genesis of life.What forms of life were able to make such a drastic change in lifestyle? The traditional view of the first terrestrial organisms is based on megafossils - relatively large specimens of essential whole plants and animals. Vascular plants, related to modern seed plants and ferns, left the first comprehensive megafossil record. Because of this, it has been commonly assumed that the sequence of terrestrialization reflected the evolution of 10 modern terrestrial ecosystems. In this view, primitive vascular plants first colonized the margins of continental waters, followed by animals that fed on the plants, and lastly by the animals that preyed on the plant-eaters. Moreover, the megafossils suggest that terrestrial life appeared and diversified explosively near the boundary between the Silurian and the Devonian periods, a little more than 400 million years ago.Recently, however, paleontologists have been taking a closer look at sediments below this Silurian- Devonian geological boundary. It turns out that some fossils can be extracted from these sediments by putting the rock in an acid bath. The technique has uncovered new evidence from sediments that were deposited near the shores of the ancient oceans - plant microfossils and microscopic pieces of small animals. In many instances, the specimens are less than one-tenth of a millimeter in diameter. Although they were entombed in the rocks for hundreds of millions of years, many of the fossils consist of the organic remains of the organism.These discovered fossils have not only revealed the existence ofpreviously unknown organisms, but have also pushed back these dates for the invasion of land by multicellular organisms. Our view about the nature of the early plants and animal communities are now being revised. And with those revisions come new speculations about the first terrestrial life-formsThe word "drastic" is closest in meaning to ________.

Xem chi tiết 583 lượt xem 6 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 .            Martin Luther King, Jf., is well- known for his work in civil rights and for his many famous speeches, among which is his moving “ I have a dream” speech. But fewer people know much about King’s childhood. M.L., as he was called, was born in 1929 in Atlanta, Georgia, at the home of his maternal grandfather. M.L.’s grandfather purchased their home on Auburn Avenue in 1909, twenty years before M.L was born. His grandfather allowed the house to be used as a meeting place for a number of organizations dedicated to the education and social advancement of blacks. M.L. grew up in the atmosphere, with his home being used as a community gathering place, and was no doubt influenced by it.           M.L.’s childhood was not especially eventfully. His father was a minister and his mother was a musician. He was the second of three children, and he attended all black schools in a black neighborhood. The neighborhood was not poor, however. Auburn Avenue was an area of banks, insurance companies, builders, jewelers, tailors, doctors, lawyers, and other businesses and services. Even in the face of Atlanta’s segregation, the district thrived. Dr. King never forgot the community spirit he had known as a child, nor did he forget the racial prejudice that was a huge barrier keeping black Atlantans from mingling with whites.M.L. was _______ by the atmosphere in which he grew up.'

Xem chi tiết 1.3 K lượt xem 6 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 .            Martin Luther King, Jf., is well- known for his work in civil rights and for his many famous speeches, among which is his moving “ I have a dream” speech. But fewer people know much about King’s childhood. M.L., as he was called, was born in 1929 in Atlanta, Georgia, at the home of his maternal grandfather. M.L.’s grandfather purchased their home on Auburn Avenue in 1909, twenty years before M.L was born. His grandfather allowed the house to be used as a meeting place for a number of organizations dedicated to the education and social advancement of blacks. M.L. grew up in the atmosphere, with his home being used as a community gathering place, and was no doubt influenced by it.           M.L.’s childhood was not especially eventfully. His father was a minister and his mother was a musician. He was the second of three children, and he attended all black schools in a black neighborhood. The neighborhood was not poor, however. Auburn Avenue was an area of banks, insurance companies, builders, jewelers, tailors, doctors, lawyers, and other businesses and services. Even in the face of Atlanta’s segregation, the district thrived. Dr. King never forgot the community spirit he had known as a child, nor did he forget the racial prejudice that was a huge barrier keeping black Atlantans from mingling with whites.From the passage we can infer that:

Xem chi tiết 333 lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C or D to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.KEEPING FIT          Bodies are made to move! They are not (31) ________ for sitting around in front of the television or reading magazines. Keeping fit doesn't mean have to be a super-athlete, and even (32) ________ exercise can give you a lot of fun. When you are fit and healthy, you will find you look better and feel better. You will develop more energy and self-confidence.Every time you move, you are exercising. The human body is designed to bend, stretch, run, jump and climb. (33) ________it does, the stronger and fitter it will become. Best of all, exercise is fun. It's what your body likes doing most-keeping on the move.Physical exercise is not only good for your body. People who take regular exercise are usually happier, more relaxed and more alert than people who sit around all day. Try an experiment-next time you are in a bad mood, go for a walk or play a ball game in the park. See how much better you feel after an hour.            A good (34) ________of achievement is yet another benefit of exercise. People feel good about themselves when they know they have improved their fitness. People who exercise regularly will tell you that they find they have more energy to enjoy life. So have (35) ________you'll soon see and feel the benefitsĐiền vào ô 35

Xem chi tiết 12.2 K lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C or D to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.KEEPING FIT          Bodies are made to move! They are not (31) ________ for sitting around in front of the television or reading magazines. Keeping fit doesn't mean have to be a super-athlete, and even (32) ________ exercise can give you a lot of fun. When you are fit and healthy, you will find you look better and feel better. You will develop more energy and self-confidence.Every time you move, you are exercising. The human body is designed to bend, stretch, run, jump and climb. (33) ________it does, the stronger and fitter it will become. Best of all, exercise is fun. It's what your body likes doing most-keeping on the move.Physical exercise is not only good for your body. People who take regular exercise are usually happier, more relaxed and more alert than people who sit around all day. Try an experiment-next time you are in a bad mood, go for a walk or play a ball game in the park. See how much better you feel after an hour.            A good (34) ________of achievement is yet another benefit of exercise. People feel good about themselves when they know they have improved their fitness. People who exercise regularly will tell you that they find they have more energy to enjoy life. So have (35) ________you'll soon see and feel the benefitsĐiền vào ô 34

Xem chi tiết 3.5 K lượt xem 6 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 .            Martin Luther King, Jf., is well- known for his work in civil rights and for his many famous speeches, among which is his moving “ I have a dream” speech. But fewer people know much about King’s childhood. M.L., as he was called, was born in 1929 in Atlanta, Georgia, at the home of his maternal grandfather. M.L.’s grandfather purchased their home on Auburn Avenue in 1909, twenty years before M.L was born. His grandfather allowed the house to be used as a meeting place for a number of organizations dedicated to the education and social advancement of blacks. M.L. grew up in the atmosphere, with his home being used as a community gathering place, and was no doubt influenced by it.           M.L.’s childhood was not especially eventfully. His father was a minister and his mother was a musician. He was the second of three children, and he attended all black schools in a black neighborhood. The neighborhood was not poor, however. Auburn Avenue was an area of banks, insurance companies, builders, jewelers, tailors, doctors, lawyers, and other businesses and services. Even in the face of Atlanta’s segregation, the district thrived. Dr. King never forgot the community spirit he had known as a child, nor did he forget the racial prejudice that was a huge barrier keeping black Atlantans from mingling with whites.Which of the following statements is NOT true?

Xem chi tiết 756 lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C or D to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.KEEPING FIT          Bodies are made to move! They are not (31) ________ for sitting around in front of the television or reading magazines. Keeping fit doesn't mean have to be a super-athlete, and even (32) ________ exercise can give you a lot of fun. When you are fit and healthy, you will find you look better and feel better. You will develop more energy and self-confidence.Every time you move, you are exercising. The human body is designed to bend, stretch, run, jump and climb. (33) ________it does, the stronger and fitter it will become. Best of all, exercise is fun. It's what your body likes doing most-keeping on the move.Physical exercise is not only good for your body. People who take regular exercise are usually happier, more relaxed and more alert than people who sit around all day. Try an experiment-next time you are in a bad mood, go for a walk or play a ball game in the park. See how much better you feel after an hour.            A good (34) ________of achievement is yet another benefit of exercise. People feel good about themselves when they know they have improved their fitness. People who exercise regularly will tell you that they find they have more energy to enjoy life. So have (35) ________you'll soon see and feel the benefitsĐiền vào ô 33

Xem chi tiết 1.7 K lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C or D to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.KEEPING FIT          Bodies are made to move! They are not (31) ________ for sitting around in front of the television or reading magazines. Keeping fit doesn't mean have to be a super-athlete, and even (32) ________ exercise can give you a lot of fun. When you are fit and healthy, you will find you look better and feel better. You will develop more energy and self-confidence.Every time you move, you are exercising. The human body is designed to bend, stretch, run, jump and climb. (33) ________it does, the stronger and fitter it will become. Best of all, exercise is fun. It's what your body likes doing most-keeping on the move.Physical exercise is not only good for your body. People who take regular exercise are usually happier, more relaxed and more alert than people who sit around all day. Try an experiment-next time you are in a bad mood, go for a walk or play a ball game in the park. See how much better you feel after an hour.            A good (34) ________of achievement is yet another benefit of exercise. People feel good about themselves when they know they have improved their fitness. People who exercise regularly will tell you that they find they have more energy to enjoy life. So have (35) ________you'll soon see and feel the benefitsĐiền vào ô 32

Xem chi tiết 1.5 K lượt xem 6 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 .            Martin Luther King, Jf., is well- known for his work in civil rights and for his many famous speeches, among which is his moving “ I have a dream” speech. But fewer people know much about King’s childhood. M.L., as he was called, was born in 1929 in Atlanta, Georgia, at the home of his maternal grandfather. M.L.’s grandfather purchased their home on Auburn Avenue in 1909, twenty years before M.L was born. His grandfather allowed the house to be used as a meeting place for a number of organizations dedicated to the education and social advancement of blacks. M.L. grew up in the atmosphere, with his home being used as a community gathering place, and was no doubt influenced by it.           M.L.’s childhood was not especially eventfully. His father was a minister and his mother was a musician. He was the second of three children, and he attended all black schools in a black neighborhood. The neighborhood was not poor, however. Auburn Avenue was an area of banks, insurance companies, builders, jewelers, tailors, doctors, lawyers, and other businesses and services. Even in the face of Atlanta’s segregation, the district thrived. Dr. King never forgot the community spirit he had known as a child, nor did he forget the racial prejudice that was a huge barrier keeping black Atlantans from mingling with whites.According to the author, M.L. _______.

Xem chi tiết 1.2 K lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C or D to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.KEEPING FIT          Bodies are made to move! They are not (31) ________ for sitting around in front of the television or reading magazines. Keeping fit doesn't mean have to be a super-athlete, and even (32) ________ exercise can give you a lot of fun. When you are fit and healthy, you will find you look better and feel better. You will develop more energy and self-confidence.Every time you move, you are exercising. The human body is designed to bend, stretch, run, jump and climb. (33) ________it does, the stronger and fitter it will become. Best of all, exercise is fun. It's what your body likes doing most-keeping on the move.Physical exercise is not only good for your body. People who take regular exercise are usually happier, more relaxed and more alert than people who sit around all day. Try an experiment-next time you are in a bad mood, go for a walk or play a ball game in the park. See how much better you feel after an hour.            A good (34) ________of achievement is yet another benefit of exercise. People feel good about themselves when they know they have improved their fitness. People who exercise regularly will tell you that they find they have more energy to enjoy life. So have (35) ________you'll soon see and feel the benefitsĐiền vào ô 31

Xem chi tiết 704 lượt xem 6 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 .            Martin Luther King, Jf., is well- known for his work in civil rights and for his many famous speeches, among which is his moving “ I have a dream” speech. But fewer people know much about King’s childhood. M.L., as he was called, was born in 1929 in Atlanta, Georgia, at the home of his maternal grandfather. M.L.’s grandfather purchased their home on Auburn Avenue in 1909, twenty years before M.L was born. His grandfather allowed the house to be used as a meeting place for a number of organizations dedicated to the education and social advancement of blacks. M.L. grew up in the atmosphere, with his home being used as a community gathering place, and was no doubt influenced by it.           M.L.’s childhood was not especially eventfully. His father was a minister and his mother was a musician. He was the second of three children, and he attended all black schools in a black neighborhood. The neighborhood was not poor, however. Auburn Avenue was an area of banks, insurance companies, builders, jewelers, tailors, doctors, lawyers, and other businesses and services. Even in the face of Atlanta’s segregation, the district thrived. Dr. King never forgot the community spirit he had known as a child, nor did he forget the racial prejudice that was a huge barrier keeping black Atlantans from mingling with whites.What is Martin Luthur King well- known for?

Xem chi tiết 2.3 K lượt xem 6 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 .            Martin Luther King, Jf., is well- known for his work in civil rights and for his many famous speeches, among which is his moving “ I have a dream” speech. But fewer people know much about King’s childhood. M.L., as he was called, was born in 1929 in Atlanta, Georgia, at the home of his maternal grandfather. M.L.’s grandfather purchased their home on Auburn Avenue in 1909, twenty years before M.L was born. His grandfather allowed the house to be used as a meeting place for a number of organizations dedicated to the education and social advancement of blacks. M.L. grew up in the atmosphere, with his home being used as a community gathering place, and was no doubt influenced by it.           M.L.’s childhood was not especially eventfully. His father was a minister and his mother was a musician. He was the second of three children, and he attended all black schools in a black neighborhood. The neighborhood was not poor, however. Auburn Avenue was an area of banks, insurance companies, builders, jewelers, tailors, doctors, lawyers, and other businesses and services. Even in the face of Atlanta’s segregation, the district thrived. Dr. King never forgot the community spirit he had known as a child, nor did he forget the racial prejudice that was a huge barrier keeping black Atlantans from mingling with whites.When was M.L. born?

Xem chi tiết 652 lượt xem 6 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 .            Martin Luther King, Jf., is well- known for his work in civil rights and for his many famous speeches, among which is his moving “ I have a dream” speech. But fewer people know much about King’s childhood. M.L., as he was called, was born in 1929 in Atlanta, Georgia, at the home of his maternal grandfather. M.L.’s grandfather purchased their home on Auburn Avenue in 1909, twenty years before M.L was born. His grandfather allowed the house to be used as a meeting place for a number of organizations dedicated to the education and social advancement of blacks. M.L. grew up in the atmosphere, with his home being used as a community gathering place, and was no doubt influenced by it.           M.L.’s childhood was not especially eventfully. His father was a minister and his mother was a musician. He was the second of three children, and he attended all black schools in a black neighborhood. The neighborhood was not poor, however. Auburn Avenue was an area of banks, insurance companies, builders, jewelers, tailors, doctors, lawyers, and other businesses and services. Even in the face of Atlanta’s segregation, the district thrived. Dr. King never forgot the community spirit he had known as a child, nor did he forget the racial prejudice that was a huge barrier keeping black Atlantans from mingling with whites.What is the passage mainly about?

Xem chi tiết 59.4 K lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C ,or D on your answer sheet to indicate the correct answer for each of the questions.           Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger to the ground and depositing a tiny amount of trail pheromone – a mixture of chemicals that delivers diverse messages as the context changes. These trails incorporate no directional information and may be followed by other ants in either direction.           Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Atta texana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth.          The vapor of the evaporating pheromone over the trail guides an ant along the way, and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space. The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail.According to the passage, the highest amount of pheromone vapor is found

Xem chi tiết 399 lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C ,or D on your answer sheet to indicate the correct answer for each of the questions.           Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger to the ground and depositing a tiny amount of trail pheromone – a mixture of chemicals that delivers diverse messages as the context changes. These trails incorporate no directional information and may be followed by other ants in either direction.           Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Atta texana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth.          The vapor of the evaporating pheromone over the trail guides an ant along the way, and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space. The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail.The word “oscillating“ in line 17 is closest in meaning to ____

Xem chi tiết 379 lượt xem 6 năm trước

Read the following passage and mark the letter A, B, C ,or D on your answer sheet to indicate the correct answer for each of the questions.           Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger to the ground and depositing a tiny amount of trail pheromone – a mixture of chemicals that delivers diverse messages as the context changes. These trails incorporate no directional information and may be followed by other ants in either direction.           Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Atta texana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth.          The vapor of the evaporating pheromone over the trail guides an ant along the way, and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space. The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail.According to the passage, how are ants guided by trail pheromones?

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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 for each of the questions.           Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger to the ground and depositing a tiny amount of trail pheromone – a mixture of chemicals that delivers diverse messages as the context changes. These trails incorporate no directional information and may be followed by other ants in either direction.           Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Atta texana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth.          The vapor of the evaporating pheromone over the trail guides an ant along the way, and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space. The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail.The author mentions the trail pheromone of the leafcutter ant in line 11 to point out

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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 for each of the questions.           Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger to the ground and depositing a tiny amount of trail pheromone – a mixture of chemicals that delivers diverse messages as the context changes. These trails incorporate no directional information and may be followed by other ants in either direction.           Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Atta texana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth.          The vapor of the evaporating pheromone over the trail guides an ant along the way, and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space. The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail.According to the passage, why do ants use different compounds as trail pheromones?

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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 for each of the questions.           Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger to the ground and depositing a tiny amount of trail pheromone – a mixture of chemicals that delivers diverse messages as the context changes. These trails incorporate no directional information and may be followed by other ants in either direction.           Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Atta texana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth.          The vapor of the evaporating pheromone over the trail guides an ant along the way, and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space. The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail.The phrase “the one” in line 8 refers to a single'

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