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Read the following text and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to 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 573 lượt xem 5 năm trước

Read the following text and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to 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?

Xem chi tiết 471 lượt xem 5 năm trước

Read the following text and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to 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 paragraph 2 to point out

Xem chi tiết 523 lượt xem 5 năm trước

Read the following text and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to 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 a trail pheromones?

Xem chi tiết 503 lượt xem 5 năm trước

Read the following text and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to 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 paragraph 2 refers to a single

Xem chi tiết 478 lượt xem 5 năm trước

Read the following text and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to 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 “intermittently” in paragraph 1 is closest in meaning to

Xem chi tiết 735 lượt xem 5 năm trước

Read the following text and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to 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.What does the passage mainly discuss?

Xem chi tiết 813 lượt xem 5 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.Oxbridge is a word made from the names Oxford and Cambridge and is used to refer (46)_____ to the universities of Oxford and Cambridge together, especially when they are being distinguished from other universities.Oxford and Cambridge are the oldest universities in Britain. They are generally alsothought to be the best universities to get a place at. An Oxbridge degree (47)_____ a good impression on many employers, and graduates of these universities may have an advantage when applying for jobs. The upper class has traditionally sent their children to Oxbridge, and many prime ministers and politicians went there. To many people, Oxford and Cambridge seem very remote places (48)_____ only the very privileged can go.The teaching system is different from that at most other universities. Students have tutorials, called supervisions at Cambridge, (49)_____ which they read their essays to their tutor. Terms are short and intense, and students are expected to prepare for them in the vacations. Final examinations at Oxford are called schools, and at Cambridge the trips. Undergraduates at Oxford and Cambridge study for a BA degree, but after a period of time graduates can (50)_____ their BA to an MA without doing any further study.Điền vào ô 50.

Xem chi tiết 892 lượt xem 5 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.Oxbridge is a word made from the names Oxford and Cambridge and is used to refer (46)_____ to the universities of Oxford and Cambridge together, especially when they are being distinguished from other universities.Oxford and Cambridge are the oldest universities in Britain. They are generally alsothought to be the best universities to get a place at. An Oxbridge degree (47)_____ a good impression on many employers, and graduates of these universities may have an advantage when applying for jobs. The upper class has traditionally sent their children to Oxbridge, and many prime ministers and politicians went there. To many people, Oxford and Cambridge seem very remote places (48)_____ only the very privileged can go.The teaching system is different from that at most other universities. Students have tutorials, called supervisions at Cambridge, (49)_____ which they read their essays to their tutor. Terms are short and intense, and students are expected to prepare for them in the vacations. Final examinations at Oxford are called schools, and at Cambridge the trips. Undergraduates at Oxford and Cambridge study for a BA degree, but after a period of time graduates can (50)_____ their BA to an MA without doing any further study.Điền vào ô 49.

Xem chi tiết 594 lượt xem 5 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.Oxbridge is a word made from the names Oxford and Cambridge and is used to refer (46)_____ to the universities of Oxford and Cambridge together, especially when they are being distinguished from other universities.Oxford and Cambridge are the oldest universities in Britain. They are generally alsothought to be the best universities to get a place at. An Oxbridge degree (47)_____ a good impression on many employers, and graduates of these universities may have an advantage when applying for jobs. The upper class has traditionally sent their children to Oxbridge, and many prime ministers and politicians went there. To many people, Oxford and Cambridge seem very remote places (48)_____ only the very privileged can go.The teaching system is different from that at most other universities. Students have tutorials, called supervisions at Cambridge, (49)_____ which they read their essays to their tutor. Terms are short and intense, and students are expected to prepare for them in the vacations. Final examinations at Oxford are called schools, and at Cambridge the trips. Undergraduates at Oxford and Cambridge study for a BA degree, but after a period of time graduates can (50)_____ their BA to an MA without doing any further study.Điền vào ô 48.

Xem chi tiết 1.1 K lượt xem 5 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.Oxbridge is a word made from the names Oxford and Cambridge and is used to refer (46)_____ to the universities of Oxford and Cambridge together, especially when they are being distinguished from other universities.Oxford and Cambridge are the oldest universities in Britain. They are generally alsothought to be the best universities to get a place at. An Oxbridge degree (47)_____ a good impression on many employers, and graduates of these universities may have an advantage when applying for jobs. The upper class has traditionally sent their children to Oxbridge, and many prime ministers and politicians went there. To many people, Oxford and Cambridge seem very remote places (48)_____ only the very privileged can go.The teaching system is different from that at most other universities. Students have tutorials, called supervisions at Cambridge, (49)_____ which they read their essays to their tutor. Terms are short and intense, and students are expected to prepare for them in the vacations. Final examinations at Oxford are called schools, and at Cambridge the trips. Undergraduates at Oxford and Cambridge study for a BA degree, but after a period of time graduates can (50)_____ their BA to an MA without doing any further study.Điền vào ô 47.

Xem chi tiết 714 lượt xem 5 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.Oxbridge is a word made from the names Oxford and Cambridge and is used to refer (46)_____ to the universities of Oxford and Cambridge together, especially when they are being distinguished from other universities.Oxford and Cambridge are the oldest universities in Britain. They are generally alsothought to be the best universities to get a place at. An Oxbridge degree (47)_____ a good impression on many employers, and graduates of these universities may have an advantage when applying for jobs. The upper class has traditionally sent their children to Oxbridge, and many prime ministers and politicians went there. To many people, Oxford and Cambridge seem very remote places (48)_____ only the very privileged can go.The teaching system is different from that at most other universities. Students have tutorials, called supervisions at Cambridge, (49)_____ which they read their essays to their tutor. Terms are short and intense, and students are expected to prepare for them in the vacations. Final examinations at Oxford are called schools, and at Cambridge the trips. Undergraduates at Oxford and Cambridge study for a BA degree, but after a period of time graduates can (50)_____ their BA to an MA without doing any further study.Điền vào ô 46.

Xem chi tiết 1 K lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the question.Alaska is disappearing slowly, but surely. It is estimated that since the 19505, as much as fifteen percent of Alaska's land area has disappeared. How can a whole state be disappearing? The problem is that Alaska’s glaciers are melting. The state has more than 100,000 glaciers. These glaciers account for about 75,000 square kilometers, or five percent, of the state’s area. That is an area of land larger than Ireland!According to a recent report by the US Geological Survey, ninety-nine percent of Alaska's glaciers are either retreating or diminishing. This diminishing seems mainly due to the increase in global temperatures. Since the 19605, the average year-round temperature has increased by almost 3°C. Additionally, the average winter temperature has increased by over 6°C. Presently, an estimated 100 cubic kilometers of ice is disappearing from Alaskan glaciers every year. It may be even more in the near future, as some scientists predict that the average world temperature could go up 4 to 7°C by the year 2100.Another problem facing Alaska is its thawing permafrost. Much of the land in Alaska used to be permanently frozen or frozen for most of the year. Now, the thawing permafrost is causing a number of problems for people living in Alaska. Roads and utility poles are collapsing as the ground around and under them warms and soften. Also, the hard permafrost that originally prevented beaches from eroding during violent storms is now melting. People who live along Alaska's coasts are being forced to relocate. For villages on small low islands, one terrible storm could wipe out the entire community.The melting permafrost and increasing temperatures are both affecting the forests of Alaska. As the permafrost under the forests melts, insects that normally do not turn up until the warmer seasons are appearing sooner. The spruce-bark beetle, for example, is increasing in numbers as a result of warmer winter temperatures. It usually takes about two years for these beetles to grow and reproduce in. very cold weather. However, due to the increase in temperatures, spruce-bark beetles are reproducing faster and damaging as many trees in one year as they previously damaged in two. If something cannot be done tochange things, Alaska's forests will not survive the turn of the century.Some scientists believe that human activity is linked to a global increase in weather temperature. Whatever the cause of rising temperatures may be, the fact remains that temperatures are warming, affecting Alaska for the worse. Horribly, this could be a preview of what will happen to the rest of the world in the next century.What is predicted in the last paragraph?

Xem chi tiết 704 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the question.Alaska is disappearing slowly, but surely. It is estimated that since the 19505, as much as fifteen percent of Alaska's land area has disappeared. How can a whole state be disappearing? The problem is that Alaska’s glaciers are melting. The state has more than 100,000 glaciers. These glaciers account for about 75,000 square kilometers, or five percent, of the state’s area. That is an area of land larger than Ireland!According to a recent report by the US Geological Survey, ninety-nine percent of Alaska's glaciers are either retreating or diminishing. This diminishing seems mainly due to the increase in global temperatures. Since the 19605, the average year-round temperature has increased by almost 3°C. Additionally, the average winter temperature has increased by over 6°C. Presently, an estimated 100 cubic kilometers of ice is disappearing from Alaskan glaciers every year. It may be even more in the near future, as some scientists predict that the average world temperature could go up 4 to 7°C by the year 2100.Another problem facing Alaska is its thawing permafrost. Much of the land in Alaska used to be permanently frozen or frozen for most of the year. Now, the thawing permafrost is causing a number of problems for people living in Alaska. Roads and utility poles are collapsing as the ground around and under them warms and soften. Also, the hard permafrost that originally prevented beaches from eroding during violent storms is now melting. People who live along Alaska's coasts are being forced to relocate. For villages on small low islands, one terrible storm could wipe out the entire community.The melting permafrost and increasing temperatures are both affecting the forests of Alaska. As the permafrost under the forests melts, insects that normally do not turn up until the warmer seasons are appearing sooner. The spruce-bark beetle, for example, is increasing in numbers as a result of warmer winter temperatures. It usually takes about two years for these beetles to grow and reproduce in. very cold weather. However, due to the increase in temperatures, spruce-bark beetles are reproducing faster and damaging as many trees in one year as they previously damaged in two. If something cannot be done tochange things, Alaska's forests will not survive the turn of the century.Some scientists believe that human activity is linked to a global increase in weather temperature. Whatever the cause of rising temperatures may be, the fact remains that temperatures are warming, affecting Alaska for the worse. Horribly, this could be a preview of what will happen to the rest of the world in the next century.The word "relocate" in paragraph 3 is closest in meaning to _____.

Xem chi tiết 808 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the question.Alaska is disappearing slowly, but surely. It is estimated that since the 19505, as much as fifteen percent of Alaska's land area has disappeared. How can a whole state be disappearing? The problem is that Alaska’s glaciers are melting. The state has more than 100,000 glaciers. These glaciers account for about 75,000 square kilometers, or five percent, of the state’s area. That is an area of land larger than Ireland!According to a recent report by the US Geological Survey, ninety-nine percent of Alaska's glaciers are either retreating or diminishing. This diminishing seems mainly due to the increase in global temperatures. Since the 19605, the average year-round temperature has increased by almost 3°C. Additionally, the average winter temperature has increased by over 6°C. Presently, an estimated 100 cubic kilometers of ice is disappearing from Alaskan glaciers every year. It may be even more in the near future, as some scientists predict that the average world temperature could go up 4 to 7°C by the year 2100.Another problem facing Alaska is its thawing permafrost. Much of the land in Alaska used to be permanently frozen or frozen for most of the year. Now, the thawing permafrost is causing a number of problems for people living in Alaska. Roads and utility poles are collapsing as the ground around and under them warms and soften. Also, the hard permafrost that originally prevented beaches from eroding during violent storms is now melting. People who live along Alaska's coasts are being forced to relocate. For villages on small low islands, one terrible storm could wipe out the entire community.The melting permafrost and increasing temperatures are both affecting the forests of Alaska. As the permafrost under the forests melts, insects that normally do not turn up until the warmer seasons are appearing sooner. The spruce-bark beetle, for example, is increasing in numbers as a result of warmer winter temperatures. It usually takes about two years for these beetles to grow and reproduce in. very cold weather. However, due to the increase in temperatures, spruce-bark beetles are reproducing faster and damaging as many trees in one year as they previously damaged in two. If something cannot be done tochange things, Alaska's forests will not survive the turn of the century.Some scientists believe that human activity is linked to a global increase in weather temperature. Whatever the cause of rising temperatures may be, the fact remains that temperatures are warming, affecting Alaska for the worse. Horribly, this could be a preview of what will happen to the rest of the world in the next century.The word “permafrost” in the third paragraph mostly means _____.

Xem chi tiết 780 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the question.Alaska is disappearing slowly, but surely. It is estimated that since the 19505, as much as fifteen percent of Alaska's land area has disappeared. How can a whole state be disappearing? The problem is that Alaska’s glaciers are melting. The state has more than 100,000 glaciers. These glaciers account for about 75,000 square kilometers, or five percent, of the state’s area. That is an area of land larger than Ireland!According to a recent report by the US Geological Survey, ninety-nine percent of Alaska's glaciers are either retreating or diminishing. This diminishing seems mainly due to the increase in global temperatures. Since the 19605, the average year-round temperature has increased by almost 3°C. Additionally, the average winter temperature has increased by over 6°C. Presently, an estimated 100 cubic kilometers of ice is disappearing from Alaskan glaciers every year. It may be even more in the near future, as some scientists predict that the average world temperature could go up 4 to 7°C by the year 2100.Another problem facing Alaska is its thawing permafrost. Much of the land in Alaska used to be permanently frozen or frozen for most of the year. Now, the thawing permafrost is causing a number of problems for people living in Alaska. Roads and utility poles are collapsing as the ground around and under them warms and soften. Also, the hard permafrost that originally prevented beaches from eroding during violent storms is now melting. People who live along Alaska's coasts are being forced to relocate. For villages on small low islands, one terrible storm could wipe out the entire community.The melting permafrost and increasing temperatures are both affecting the forests of Alaska. As the permafrost under the forests melts, insects that normally do not turn up until the warmer seasons are appearing sooner. The spruce-bark beetle, for example, is increasing in numbers as a result of warmer winter temperatures. It usually takes about two years for these beetles to grow and reproduce in. very cold weather. However, due to the increase in temperatures, spruce-bark beetles are reproducing faster and damaging as many trees in one year as they previously damaged in two. If something cannot be done tochange things, Alaska's forests will not survive the turn of the century.Some scientists believe that human activity is linked to a global increase in weather temperature. Whatever the cause of rising temperatures may be, the fact remains that temperatures are warming, affecting Alaska for the worse. Horribly, this could be a preview of what will happen to the rest of the world in the next century.According to the report by the US Geological Survey, which of the following is NOT true about Alaska?

Xem chi tiết 678 lượt xem 5 năm trước

Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the question.Alaska is disappearing slowly, but surely. It is estimated that since the 19505, as much as fifteen percent of Alaska's land area has disappeared. How can a whole state be disappearing? The problem is that Alaska’s glaciers are melting. The state has more than 100,000 glaciers. These glaciers account for about 75,000 square kilometers, or five percent, of the state’s area. That is an area of land larger than Ireland!According to a recent report by the US Geological Survey, ninety-nine percent of Alaska's glaciers are either retreating or diminishing. This diminishing seems mainly due to the increase in global temperatures. Since the 19605, the average year-round temperature has increased by almost 3°C. Additionally, the average winter temperature has increased by over 6°C. Presently, an estimated 100 cubic kilometers of ice is disappearing from Alaskan glaciers every year. It may be even more in the near future, as some scientists predict that the average world temperature could go up 4 to 7°C by the year 2100.Another problem facing Alaska is its thawing permafrost. Much of the land in Alaska used to be permanently frozen or frozen for most of the year. Now, the thawing permafrost is causing a number of problems for people living in Alaska. Roads and utility poles are collapsing as the ground around and under them warms and soften. Also, the hard permafrost that originally prevented beaches from eroding during violent storms is now melting. People who live along Alaska's coasts are being forced to relocate. For villages on small low islands, one terrible storm could wipe out the entire community.The melting permafrost and increasing temperatures are both affecting the forests of Alaska. As the permafrost under the forests melts, insects that normally do not turn up until the warmer seasons are appearing sooner. The spruce-bark beetle, for example, is increasing in numbers as a result of warmer winter temperatures. It usually takes about two years for these beetles to grow and reproduce in. very cold weather. However, due to the increase in temperatures, spruce-bark beetles are reproducing faster and damaging as many trees in one year as they previously damaged in two. If something cannot be done tochange things, Alaska's forests will not survive the turn of the century.Some scientists believe that human activity is linked to a global increase in weather temperature. Whatever the cause of rising temperatures may be, the fact remains that temperatures are warming, affecting Alaska for the worse. Horribly, this could be a preview of what will happen to the rest of the world in the next century.As mentioned in the first paragraph, the glaciers in Alaska made up _____.

Xem chi tiết 628 lượt xem 5 năm trước