Danh sách câu hỏi ( Có 87,242 câu hỏi trên 1,745 trang )

Read the following passage and mark the letter A, B, C, or D to indicate the correct answer. The advent of the Internet may be one of the most important technological developments in recent years. Never before have so many people had access to so many different sources of information. For all of the Internet’s advantages, however, people are currently becoming aware of some of its drawbacks and are looking for creative solutions. Among the current problems, which include a general lack of reliability and numerous security concerns, the most crucial is speed. First of all, the Internet has grown very quickly. In 1990, only a few academics had ever heard of the Internet. In 1996, over 50 million people used it. Every year, the number of people with access to the Internet doubles. The rapid growth has been a problem. The computer systems which run the Internet have not been able to keep up with the demand. Also, sometimes, a request for information must pass through many routing computers before the information can be obtained. A request for information made in Paris might have to go through computers in New York, Los Angeles and Tokyo in order to obtain the required information. Consequently, the service is often slow and unpredictable. Service also tends to be worse when the Internet is busiest - during the business day of the Western Hemisphere - which is also when companies need its service the most.Some people are trying to harness the power of networked computers in such a way as to avoid this problem. In 1995, a group of American universities banded together to form what has come to be known as Internet II. Internet II is a smaller, more specialized system intended for academic use. Since it is more specialized, fewer users are allowed access. Consequently, the time required to receive information has decreased. Businesses are beginning to explore a possible analogue to the Internet II. Many businesses are creating their own “Intranets”. These are systems that can only be used by the members of the same company. In theory, fewer users should translate into a faster system. Intranets are very useful for large national and international companies whose branches need to share information. Another benefit of an Intranet is an increased amount of security. Since only company employees have access to the information on the Intranet, their information is protected from competitors. While there is little doubt that the Internet will eventually be a fast and reliable service, industry and the academic community have taken their own steps toward making more practical global networks. In the passage, which of the following ts NOT true of the Internet?

Xem chi tiết 361 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.            Successful students often do the followings while studying. First they have an overview before reading. Next, they look for important information and pay greater attention to it (which often needs jumping forward or backward to process information). They also relate important points to one another. Also, they activate and use their prior knowledge. When they realize that their understanding is not good, they do not wait to change strategies. Last, they can monitor understanding and take action to correct or “ fix-up” mistakes in comprehension.          Conversely, students with low academic achievement often demonstrate ineffective study skills. They tend to assume a passive role in learning and rely on others(e.g, teachers, parents) to monitor their studying. For example, low-achieving students often do not monitor their understanding of content, they may not be aware of the purpose of studying, and their show little evidence of looking back, or employing “fix-up” strategies to fix understanding problems. Students who struggle with learning new information seem to be unaware that they must extent beyond simply reading the content to understand and remember it. Children with learning disabilities do not plan and judge the quality off their studying. Their studying may be disorganized. Students with learning problems face challenges with personal organization as well. They often have difficulty keeping track of materials and assignments, following directions, and completing work on time. Unlike good student who employ a variety of study skills in a flexible yet purposeful manner, low-achieving students use a restricted range of skills. They can not explain why good study strategies are important for learning, and they tend to use the same, often ineffective, study approach for all learning tasks, ignoring task content, structure of difficulty.What is the topic of the passage?

Xem chi tiết 5.1 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.We find that bright children are rarely held back by mixed-ability teaching. On the contrary, both their knowledge and experience are enriched. We feel that there are many disadvantages in streaming pupils. It does not take into account the fact that children develop at different rates. It can have a bad effect on both the bright and the not-so-bright child. After all, it can be quite discouraging to be at the bottom of the top grade!Besides, it is rather unreal to grade people just according to their intellectual ability. This is only one aspect of their total personality. We are concerned to develop the abilities of all our pupils to the full, not just their academic ability. We also value personal qualities and social skills, and we find that mixed-ability teaching contributes to all these aspects of learning. In our classroom, we work in various ways. The pupils often work in groups; this gives them the opportunity to learn to co-operate, to share, and to develop leadership skills. They also learn how to cope with the personal problems as well as learning how to think, to make decisions, to analyze and evaluate, to communicate effectively. The pupils learn from each other as well as from the teachers. Sometimes the pupils work in pairs; sometimes the work on individual tasks and assignments, they can do this at their own speed. They also have some formal class teaching when this is appropriate. We encourage our pupils to use the library, and we teach them the skills they need in order to do this effectively. An advanced pupil can do advanced works; it does not matter what age the child is. We expect our pupils to do their best, not their least, and we give them every encouragement to attain this goal. According to the passage, which of the following is NOT true?

Xem chi tiết 354 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.We find that bright children are rarely held back by mixed-ability teaching. On the contrary, both their knowledge and experience are enriched. We feel that there are many disadvantages in streaming pupils. It does not take into account the fact that children develop at different rates. It can have a bad effect on both the bright and the not-so-bright child. After all, it can be quite discouraging to be at the bottom of the top grade!Besides, it is rather unreal to grade people just according to their intellectual ability. This is only one aspect of their total personality. We are concerned to develop the abilities of all our pupils to the full, not just their academic ability. We also value personal qualities and social skills, and we find that mixed-ability teaching contributes to all these aspects of learning. In our classroom, we work in various ways. The pupils often work in groups; this gives them the opportunity to learn to co-operate, to share, and to develop leadership skills. They also learn how to cope with the personal problems as well as learning how to think, to make decisions, to analyze and evaluate, to communicate effectively. The pupils learn from each other as well as from the teachers. Sometimes the pupils work in pairs; sometimes the work on individual tasks and assignments, they can do this at their own speed. They also have some formal class teaching when this is appropriate. We encourage our pupils to use the library, and we teach them the skills they need in order to do this effectively. An advanced pupil can do advanced works; it does not matter what age the child is. We expect our pupils to do their best, not their least, and we give them every encouragement to attain this goal. In the passage, the author’s attitude towards “mixed-ability teaching” is_____.

Xem chi tiết 395 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.We find that bright children are rarely held back by mixed-ability teaching. On the contrary, both their knowledge and experience are enriched. We feel that there are many disadvantages in streaming pupils. It does not take into account the fact that children develop at different rates. It can have a bad effect on both the bright and the not-so-bright child. After all, it can be quite discouraging to be at the bottom of the top grade!Besides, it is rather unreal to grade people just according to their intellectual ability. This is only one aspect of their total personality. We are concerned to develop the abilities of all our pupils to the full, not just their academic ability. We also value personal qualities and social skills, and we find that mixed-ability teaching contributes to all these aspects of learning. In our classroom, we work in various ways. The pupils often work in groups; this gives them the opportunity to learn to co-operate, to share, and to develop leadership skills. They also learn how to cope with the personal problems as well as learning how to think, to make decisions, to analyze and evaluate, to communicate effectively. The pupils learn from each other as well as from the teachers. Sometimes the pupils work in pairs; sometimes the work on individual tasks and assignments, they can do this at their own speed. They also have some formal class teaching when this is appropriate. We encourage our pupils to use the library, and we teach them the skills they need in order to do this effectively. An advanced pupil can do advanced works; it does not matter what age the child is. We expect our pupils to do their best, not their least, and we give them every encouragement to attain this goal. In paragraph 1, “streaming pupils"________.

Xem chi tiết 615 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.We find that bright children are rarely held back by mixed-ability teaching. On the contrary, both their knowledge and experience are enriched. We feel that there are many disadvantages in streaming pupils. It does not take into account the fact that children develop at different rates. It can have a bad effect on both the bright and the not-so-bright child. After all, it can be quite discouraging to be at the bottom of the top grade!Besides, it is rather unreal to grade people just according to their intellectual ability. This is only one aspect of their total personality. We are concerned to develop the abilities of all our pupils to the full, not just their academic ability. We also value personal qualities and social skills, and we find that mixed-ability teaching contributes to all these aspects of learning. In our classroom, we work in various ways. The pupils often work in groups; this gives them the opportunity to learn to co-operate, to share, and to develop leadership skills. They also learn how to cope with the personal problems as well as learning how to think, to make decisions, to analyze and evaluate, to communicate effectively. The pupils learn from each other as well as from the teachers. Sometimes the pupils work in pairs; sometimes the work on individual tasks and assignments, they can do this at their own speed. They also have some formal class teaching when this is appropriate. We encourage our pupils to use the library, and we teach them the skills they need in order to do this effectively. An advanced pupil can do advanced works; it does not matter what age the child is. We expect our pupils to do their best, not their least, and we give them every encouragement to attain this goal. Which of the following statements can best summarize the main idea of the passage?

Xem chi tiết 570 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.We find that bright children are rarely held back by mixed-ability teaching. On the contrary, both their knowledge and experience are enriched. We feel that there are many disadvantages in streaming pupils. It does not take into account the fact that children develop at different rates. It can have a bad effect on both the bright and the not-so-bright child. After all, it can be quite discouraging to be at the bottom of the top grade!Besides, it is rather unreal to grade people just according to their intellectual ability. This is only one aspect of their total personality. We are concerned to develop the abilities of all our pupils to the full, not just their academic ability. We also value personal qualities and social skills, and we find that mixed-ability teaching contributes to all these aspects of learning. In our classroom, we work in various ways. The pupils often work in groups; this gives them the opportunity to learn to co-operate, to share, and to develop leadership skills. They also learn how to cope with the personal problems as well as learning how to think, to make decisions, to analyze and evaluate, to communicate effectively. The pupils learn from each other as well as from the teachers. Sometimes the pupils work in pairs; sometimes the work on individual tasks and assignments, they can do this at their own speed. They also have some formal class teaching when this is appropriate. We encourage our pupils to use the library, and we teach them the skills they need in order to do this effectively. An advanced pupil can do advanced works; it does not matter what age the child is. We expect our pupils to do their best, not their least, and we give them every encouragement to attain this goal. The phrase "held back” in paragraph 1 means________.

Xem chi tiết 277 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.We find that bright children are rarely held back by mixed-ability teaching. On the contrary, both their knowledge and experience are enriched. We feel that there are many disadvantages in streaming pupils. It does not take into account the fact that children develop at different rates. It can have a bad effect on both the bright and the not-so-bright child. After all, it can be quite discouraging to be at the bottom of the top grade! Besides, it is rather unreal to grade people just according to their intellectual ability. This is only one aspect of their total personality. We are concerned to develop the abilities of all our pupils to the full, not just their academic ability. We also value personal qualities and social skills, and we find that mixed-ability teaching contributes to all these aspects of learning. In our classroom, we work in various ways. The pupils often work in groups; this gives them the opportunity to learn to co-operate, to share, and to develop leadership skills. They also learn how to cope with the personal problems as well as learning how to think, to make decisions, to analyze and evaluate, to communicate effectively. The pupils learn from each other as well as from the teachers. Sometimes the pupils work in pairs; sometimes the work on individual tasks and assignments, they can do this at their own speed. They also have some formal class teaching when this is appropriate. We encourage our pupils to use the library, and we teach them the skills they need in order to do this effectively. An advanced pupil can do advanced works; it does not matter what age the child is. We expect our pupils to do their best, not their least, and we give them every encouragement to attain this goal. As it can be inferred from the passage, which of the following is an advantage of mixed-ability teaching?

Xem chi tiết 798 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.We find that bright children are rarely held back by mixed-ability teaching. On the contrary, both their knowledge and experience are enriched. We feel that there are many disadvantages in streaming pupils. It does not take into account the fact that children develop at different rates. It can have a bad effect on both the bright and the not-so-bright child. After all, it can be quite discouraging to be at the bottom of the top grade! Besides, it is rather unreal to grade people just according to their intellectual ability. This is only one aspect of their total personality. We are concerned to develop the abilities of all our pupils to the full, not just their academic ability. We also value personal qualities and social skills, and we find that mixed-ability teaching contributes to all these aspects of learning. In our classroom, we work in various ways. The pupils often work in groups; this gives them the opportunity to learn to co-operate, to share, and to develop leadership skills. They also learn how to cope with the personal problems as well as learning how to think, to make decisions, to analyze and evaluate, to communicate effectively. The pupils learn from each other as well as from the teachers. Sometimes the pupils work in pairs; sometimes the work on individual tasks and assignments, they can do this at their own speed. They also have some formal class teaching when this is appropriate. We encourage our pupils to use the library, and we teach them the skills they need in order to do this effectively. An advanced pupil can do advanced works; it does not matter what age the child is. We expect our pupils to do their best, not their least, and we give them every encouragement to attain this goal. The author’s purpose of writing this passage is to_______.

Xem chi tiết 0.9 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 24 to 28.A surprising number of popular spectator sports, for example football or baseball, (24)______ in Europe or the USA in the nineteenth century. This did not happen by chance. It was the (25) ______ of changes in the way people lived in those places at that time. Until then, more people lived In the country than in towns. They worked in small groups and had no regular time off. All this changed with the growth of factories and industry in the nineteenth century, first in Europe and (26) ______. In the USA. For the first time, most people began to live in towns, and they found themselves with regular free time. They had more leisure time than ever before. This resulted in the need for organized entertainment. Suitable games developed or were invented, typically team games, in which the crowd could (27) ______ sides and become involved. This gave people some of the entertainment they need in their free time. The recent explosion in TV, with the introduction of satellite and cable channels, has caused an increase in (28) ______ for sports as entertainment. The money TV has broughtto games such as football, tennis and baseball means that spectator sports will certainly go on playing an important part in our lives.Điền vào ô 28

Xem chi tiết 709 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 24 to 28.A surprising number of popular spectator sports, for example football or baseball, (24)______ in Europe or the USA in the nineteenth century. This did not happen by chance. It was the (25) ______ of changes in the way people lived in those places at that time. Until then, more people lived In the country than in towns. They worked in small groups and had no regular time off. All this changed with the growth of factories and industry in the nineteenth century, first in Europe and (26) ______. In the USA. For the first time, most people began to live in towns, and they found themselves with regular free time. They had more leisure time than ever before. This resulted in the need for organized entertainment. Suitable games developed or were invented, typically team games, in which the crowd could (27) ______ sides and become involved. This gave people some of the entertainment they need in their free time. The recent explosion in TV, with the introduction of satellite and cable channels, has caused an increase in (28) ______ for sports as entertainment. The money TV has broughtto games such as football, tennis and baseball means that spectator sports will certainly go on playing an important part in our lives.Điền vào ô 27

Xem chi tiết 2.6 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 24 to 28.A surprising number of popular spectator sports, for example football or baseball, (24)______ in Europe or the USA in the nineteenth century. This did not happen by chance. It was the (25) ______ of changes in the way people lived in those places at that time. Until then, more people lived In the country than in towns. They worked in small groups and had no regular time off. All this changed with the growth of factories and industry in the nineteenth century, first in Europe and (26) ______. In the USA. For the first time, most people began to live in towns, and they found themselves with regular free time. They had more leisure time than ever before. This resulted in the need for organized entertainment. Suitable games developed or were invented, typically team games, in which the crowd could (27) ______ sides and become involved. This gave people some of the entertainment they need in their free time. The recent explosion in TV, with the introduction of satellite and cable channels, has caused an increase in (28) ______ for sports as entertainment. The money TV has broughtto games such as football, tennis and baseball means that spectator sports will certainly go on playing an important part in our lives.Điền vào ô 26

Xem chi tiết 310 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 24 to 28.A surprising number of popular spectator sports, for example football or baseball, (24)______ in Europe or the USA in the nineteenth century. This did not happen by chance. It was the (25) ______ of changes in the way people lived in those places at that time. Until then, more people lived In the country than in towns. They worked in small groups and had no regular time off. All this changed with the growth of factories and industry in the nineteenth century, first in Europe and (26) ______. In the USA. For the first time, most people began to live in towns, and they found themselves with regular free time. They had more leisure time than ever before. This resulted in the need for organized entertainment. Suitable games developed or were invented, typically team games, in which the crowd could (27) ______ sides and become involved. This gave people some of the entertainment they need in their free time. The recent explosion in TV, with the introduction of satellite and cable channels, has caused an increase in (28) ______ for sports as entertainment. The money TV has broughtto games such as football, tennis and baseball means that spectator sports will certainly go on playing an important part in our lives.Điền vào ô 25

Xem chi tiết 640 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 24 to 28.A surprising number of popular spectator sports, for example football or baseball, (24)______ in Europe or the USA in the nineteenth century. This did not happen by chance. It was the (25) ______ of changes in the way people lived in those places at that time. Until then, more people lived In the country than in towns. They worked in small groups and had no regular time off. All this changed with the growth of factories and industry in the nineteenth century, first in Europe and (26) ______. In the USA. For the first time, most people began to live in towns, and they found themselves with regular free time. They had more leisure time than ever before. This resulted in the need for organized entertainment. Suitable games developed or were invented, typically team games, in which the crowd could (27) ______ sides and become involved. This gave people some of the entertainment they need in their free time. The recent explosion in TV, with the introduction of satellite and cable channels, has caused an increase in (28) ______ for sports as entertainment. The money TV has broughtto games such as football, tennis and baseball means that spectator sports will certainly go on playing an important part in our lives.Điền vào ô 24

Xem chi tiết 1.3 K lượt xem 6 năm trước

Mark the letter a, B, C, or D on your answer sheet to indicate the sentence that is closest meaning to each of the following questions or indicate the correct answer to each of them from 1 to 7 It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? When a species is no longer adapted to a changed environment, it may perish. The exact causes of a species’ death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be able to adapt. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species.The fossil record reveals that extinction has occurred throughout the history of Earth. Recent analyses have also revealed that on some occasions many species become extinct at the same time- a mass extinction. One of the best- known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when appropriately 95 percent of all species died. Mass extinction can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. If, for example, something were to happen to destroy much of the plankton in the oceans, then the oxygen content of Earth would drop, affection even organisms not living in the ocean. Such a change would probably lead to a mass extinction.One interesting, and controversial, finding is that extinctions during the past 250 million years have tended to be more intense every 26 million years. This periodic extinction might be due to intersection of the Earth’s orbit with a cloud of comets, but this theory is purely speculative. Some researchers have also speculated that extinction may often be random. That is, certain species may be eliminated and others may survive for no particular reason. A species’ survival may have nothing to do with its ability to adapt. If so, some of evolutionary history may reflect a sequence of essentially random events.According to the passage, it is believed that the largest extinction of a species occurred

Xem chi tiết 2 K lượt xem 6 năm trước

Mark the letter a, B, C, or D on your answer sheet to indicate the sentence that is closest meaning to each of the following questions or indicate the correct answer to each of them from 1 to 7 It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? When a species is no longer adapted to a changed environment, it may perish. The exact causes of a species’ death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be able to adapt. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species.The fossil record reveals that extinction has occurred throughout the history of Earth. Recent analyses have also revealed that on some occasions many species become extinct at the same time- a mass extinction. One of the best- known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when appropriately 95 percent of all species died. Mass extinction can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. If, for example, something were to happen to destroy much of the plankton in the oceans, then the oxygen content of Earth would drop, affection even organisms not living in the ocean. Such a change would probably lead to a mass extinction.One interesting, and controversial, finding is that extinctions during the past 250 million years have tended to be more intense every 26 million years. This periodic extinction might be due to intersection of the Earth’s orbit with a cloud of comets, but this theory is purely speculative. Some researchers have also speculated that extinction may often be random. That is, certain species may be eliminated and others may survive for no particular reason. A species’ survival may have nothing to do with its ability to adapt. If so, some of evolutionary history may reflect a sequence of essentially random events.According to paragraph 2, evidence from fossil suggests that

Xem chi tiết 479 lượt xem 6 năm trước

Mark the letter a, B, C, or D on your answer sheet to indicate the sentence that is closest meaning to each of the following questions or indicate the correct answer to each of them from 1 to 7 It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? When a species is no longer adapted to a changed environment, it may perish. The exact causes of a species’ death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be able to adapt. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species.The fossil record reveals that extinction has occurred throughout the history of Earth. Recent analyses have also revealed that on some occasions many species become extinct at the same time- a mass extinction. One of the best- known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when appropriately 95 percent of all species died. Mass extinction can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. If, for example, something were to happen to destroy much of the plankton in the oceans, then the oxygen content of Earth would drop, affection even organisms not living in the ocean. Such a change would probably lead to a mass extinction.One interesting, and controversial, finding is that extinctions during the past 250 million years have tended to be more intense every 26 million years. This periodic extinction might be due to intersection of the Earth’s orbit with a cloud of comets, but this theory is purely speculative. Some researchers have also speculated that extinction may often be random. That is, certain species may be eliminated and others may survive for no particular reason. A species’ survival may have nothing to do with its ability to adapt. If so, some of evolutionary history may reflect a sequence of essentially random events.Why is “plankton” mentioned in the second paragraph?

Xem chi tiết 3.2 K lượt xem 6 năm trước

Mark the letter a, B, C, or D on your answer sheet to indicate the sentence that is closest meaning to each of the following questions or indicate the correct answer to each of them from 1 to 7 It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? When a species is no longer adapted to a changed environment, it may perish. The exact causes of a species’ death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be able to adapt. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species.The fossil record reveals that extinction has occurred throughout the history of Earth. Recent analyses have also revealed that on some occasions many species become extinct at the same time- a mass extinction. One of the best- known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when appropriately 95 percent of all species died. Mass extinction can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. If, for example, something were to happen to destroy much of the plankton in the oceans, then the oxygen content of Earth would drop, affection even organisms not living in the ocean. Such a change would probably lead to a mass extinction.One interesting, and controversial, finding is that extinctions during the past 250 million years have tended to be more intense every 26 million years. This periodic extinction might be due to intersection of the Earth’s orbit with a cloud of comets, but this theory is purely speculative. Some researchers have also speculated that extinction may often be random. That is, certain species may be eliminated and others may survive for no particular reason. A species’ survival may have nothing to do with its ability to adapt. If so, some of evolutionary history may reflect a sequence of essentially random events.The underlined word “demise” is closest in meaning to

Xem chi tiết 425 lượt xem 6 năm trước