及答案解析：Explaining Dinosaur
Extinction!为了帮助同学们顺利备考托福考试，所以
paragraph 1
Dinosaurs rapidly became extinct about 65 million years ago as part of a mass extinction known as the K-T event, because it is associated with a geological signature known as the K-T boundary, usually a thin band of sedimentation found in various parts of the world (K is the traditional abbreviation for the Cretaceous, derived from the German name Kreidezeit). Many explanations have been proposed for why dinosaurs became extinct. For example, some have blamed dinosaur extinction on the development of flowering plants, which were supposedly more difficult to digest and could have caused constipation or indigestion—except that flowering plants first evolved in the Early Cretaceous, about 60 million years before the dinosaurs died out. In fact, several scientists have suggested that the duckbill dinosaurs and homed dinosaurs, with their complex battery of grinding teeth, evolved to exploit this new resource of rapidly growing flowering plants Others have blamed extinction on competition from the mammals, which allegedly ate all the dinosaur eggs—except that mammals and dinosaurs appeared at the same time in the Late Triassic, about 190 million years ago, and there is no reason to believe that mammals suddenly acquired a taste for dinosaur eggs after 120 million years of coexistence Some explanations (such as the one stating that dinosaurs all died of diseases) fail because there is no way to scientifically test them, and they cannot move beyond the realm of speculation and guesswork.
1. In paragraph 1, why does the author include a discussion of when flowering plants evolved?
【事实信息题】
A. To help explain why some scientists believe that the development of flowering plants led to dinosaur extinction
B. To cast doubt on the theory that the development of flowering plants caused dinosaurs to become extinct
C. To suggest that dinosaurs were able to survive for as long as they did because of the availability of flowering plants
D. To emphasize that duckbill dinosaurs and horned dinosaurs were the first dinosaurs to become extinct
答案：B
解析：根据flowering plants evolved定位至except that flowering plants first evolved in the Early Cretaceous, 看其前面一句话Many explanations have been proposed for why dinosaurs became extinct. For example, some have blamed dinosaur extinction on the development of flowering plants,作者提及开花植物的原因就是为了怀疑一些说开花植物导致恐龙灭绝的理论，所以可知B选项正确。
2. The word “allegedly” in the passage is closest in meaning to 【词汇题】
A. inevitably
B. gradually
C. Supposedly
D. Increasingly
答案：C
解析：allegedly, 依其申述，据说，据称。
Inevitably, 不可避免地。Gradually, 渐渐地。Supposedly, 按照推测。Increasingly, 增加地。所以C选项正确。
3. According to paragraph 1 the extinction of the dinosaurs is unlikely to have been the result of competition from mammals because 【事实信息题】
A. mammals would not have been capable of eating dinosaur eggs
B. mammals did not appear in any significant numbers until after the Late Triassic
C. mammals and dinosaurs did not, in fact, compete for any of the same resources
D. mammals and dinosaurs lived together for roughly 120 million years before the extinction
答案：D
解析：根据competition from mammals定位至原文and there is no reason to believe that mammals suddenly acquired a taste for dinosaur eggs after 120 million years of coexistence,可知哺乳动物之间的竞争并不会成为恐龙灭绝的原因是因为哺乳动物和恐龙一起共存了一亿两千万年，所以D选项正确。
paragraph 2
This focus on explaining dinosaur extinction misses an important point the extinction at the end of the Cretaceous was a global event that killed off organisms up and down the food chain. It wiped out many kinds of plankton in the ocean and many marine organisms that lived on the plankton at the base of the food chain. These included a variety of clams and snails, and especially the ammonites, a group of shelled squidlike creatures that dominated the Mesozoic seas and had survived many previous mass extinctions. The K-T event marked the end of the marine reptiles, such as the mosasaurs and the plesiosaurs, which were the largest creatures that had ever lived in the seas and which ruled the seas long before whales evolved. On land, there was also a crisis among the land plants, in addition to the disappearance of dinosaurs. So any event that can explain the destruction of the base of the food chain (plankton in the ocean, plants on land) can better explain what happened to organisms at the top of the food chain, such as the dinosaurs. By contrast, any explanation that focuses strictly on the dinosaurs completely misses the point The Cretaceous extinctions were a global phenomenon, and dinosaurs were just a part of a bigger picture.
本文是托福tpo42阅读题目及答案解析：Explaining Dinosaur Extinction。
paragraph 3
According to one theory, the Age of Dinosaurs ended suddenly 65 million years ago when a giant rock from space plummeted to Earth. Estimated to be ten to fifteen kilometers in diameter, this bolide (either a comet or an asteroid) was traveling at cosmic speeds of 20-70 kilometers per second, or 45,000-156,000 miles per hour. Such a huge mass traveling at such tremendous speeds carries an enormous amount of energy. When the bolide struck this energy was released and generated a huge shock wave that leveled everything for thousands of kilometers around the impact and caused most of the landscape to burst into flames. The bolide struck an area of the Yucatan Peninsula of Mexico known as Chicxulub, excavating a crater 15-20 kilometers deep and at least 170 kilometers in diameter. The impact displaced huge volumes of seawater, causing much flood damage in the Caribbean. Meanwhile, the bolide itself excavated 100 cubic kilometers of rock and debris from the site, which rose to an altitude of 100 kilometers. Most of it fell back immediately, but some of it remained as dust in the atmosphere for months. This material, along with the smoke from the fires, shrouded Earth, creating a form of nuclear winter. According to computerized climate models, global temperatures fell to near the freezing point, photosynthesis halted, and most plants on land and in the sea died. With the bottom of the food chain destroyed, dinosaurs could not survive.
4. According to paragraph 2, what is problematic about some scientists' focus on dinosaur extinction? 【事实信息题】
A. Dinosaurs became extinct so long ago that no theory about their disappearance can be proven scientifically.
B. Dinosaurs were not the only organisms that went extinct at the end of the Cretaceous period.
C. More marine organisms went extinct during the Cretaceous than did dinosaur species.
D. It is more important to understand how plankton and other marine organisms came to thrive during the Cretaceous period.
答案：B
解析：根据原文This focus on explaining dinosaur extinction misses an important point the extinction at the end of the Cretaceous was a global event that killed off organisms up and down the food chain.可知，灭绝的生物并非只有恐龙，还有很多食物链上的生物体。所以B选项正确。
5. According to paragraph 2, each of the following became extinct during the K-T event EXCEPT
【否定事实信息题】
A. early species of whales
B. marine reptiles
C. various species of clams
D. many species of land plants
答案：A
解析：根据原文The K-T event marked the end of the marine reptiles ,对应B选项。These included a variety of clams and snails,对应C选项。On land, there was also a crisis among the land plants,对应D选项。所以选择A选项。
6. What makes the extinction of “the ammonites” especially significant? 【事实信息题】
A. They were among the largest creatures that ever lived.
B. They existed at the lowest level of the food chain.
C. They had been able to survive in the Mesozoic seas.
D. They had survived many previous mass extinctions.
答案：D
解析：根据the ammonites定位至原文and especially the ammonites, a group of shelled squid like creatures that dominated the Mesozoic seas and had survived many previous mass extinctions.可知D选项正确。
7. The word “halted” in the passage is closest in meaning to 【词汇题】
A. slowed
B. stopped
C. contracted
D. declined
答案：B
解析：halted, 停止，休息。
Slowed, 减慢。Stopped, 停止。Contracted, 感染，收缩，订约。Declined, 减少。所以B选项正确。
8. The word “strictly" in the passage is closest in meaning to 【词汇题】
A. exclusively
B. mainly
C. initially
D. Wrongly
答案：A
解析：strictly, 严格地。
Exclusively, 唯一地，专有地。Mainly, 主要地。Initially, 最初。Wrongly, 错误地。所以A选项正确。
9. The word “crisis” in the passage is closest in meaning to 【词汇题】
A. collapse
B. disturbance
C. critical situation
D. loss
答案：C
解析：crisis, 危机，决定性时刻。
Collapse, 倒塌，衰竭。Disturbance, 干扰，骚乱。Critical situation, 紧急情况。Loss, 亏损，遗失。所以C选项正确。
10. How does paragraph 3 relate to paragraph 2? 【组织结构题】
A. Paragraph 3 provides an alternative explanation to the one provided in paragraph 2.
B. Paragraph 3 provides an explanation that satisfies the conditions set forth in paragraph 2.
C. Paragraph 3 provides the facts to support the theory presented in paragraph 2.
D. Paragraph 3 presents a theory that calls into question the position described in paragraph 2.
答案：B
解析：根据原文The Cretaceous extinctions were a global phenomenon可知，第二段主要讲白垩纪灭绝事件是一个全球现象，第三段继续解释另外一个理论，在六千五百万年前，当太空里的一个巨大的石头垂直落向地球时，恐龙时代就突然结束了。继而以火流星坠落展开详细解释。所以可知B选项正确。
paragraph 3
According to one theory, the Age of Dinosaurs ended suddenly 65 million years ago when a giant rock from space plummeted to Earth. Estimated to be ten to fifteen kilometers in diameter, this bolide (either a comet or an asteroid) was traveling at cosmic speeds of 20-70 kilometers per second, or 45,000-156,000 miles per hour. Such a huge mass traveling at such tremendous speeds carries an enormous amount of energy. When the bolide struck this energy was released and generated a huge shock wave that leveled everything for thousands of kilometers around the impact and caused most of the landscape to burst into flames. The bolide struck an area of the Yucatan Peninsula of Mexico known as Chicxulub, excavating a crater 15-20 kilometers deep and at least 170 kilometers in diameter. The impact displaced huge volumes of seawater, causing much flood damage in the Caribbean. Meanwhile, the bolide itself excavated 100 cubic kilometers of rock and debris from the site, which rose to an altitude of 100 kilometers. Most of it fell back immediately, but some of it remained as dust in the atmosphere for months. This material, along with the smoke from the fires, shrouded Earth, creating a form of nuclear winter. According to computerized climate models, global temperatures fell to near the freezing point, photosynthesis halted, and most plants on land and in the sea died. With the bottom of the food chain destroyed, dinosaurs could not survive.
11. Paragraph 3 answers all of the following questions EXCEPT: 【否定事实信息题】
A. Why did the bolide fall to Earth?
B. How fast was the bolide traveling?
C. How was the bolide capable of generating a shock wave?
D. How did the bolide cause flood damage to the Caribbean?
答案：A
解析：原文this bolide (either a comet or an asteroid) was traveling at cosmic speeds of 20-70 kilometers per second, or 45,000-156,000 miles per hour.对应B选项。Such a huge mass traveling at such tremendous speeds carries an enormous amount of energy. When the bolide struck this energy was released and generated a huge shock wave.对应C选项。The impact displaced huge volumes of seawater, causing much flood damage in the Caribbean.对应D选项。A选项为什么火流星会落向地球没有在原文中提及，所以选择A选项。
12. Paragraph 3 strongly suggests that if the bolide impact theory is correct, the majority of the extinctions associated with the K-T event resulted from 【事实信息题】
A. sunlight being blocked for months by dust and smoke in Earth's atmosphere
B. widespread flooding that followed the displacement of huge volumes of seawater
C. the leveling of the landscape by the shock wave that was generated when the bolide struck Earth
D. the rise in global temperatures caused by the fires that burned much of the landscape
答案：A
解析：根据原文Most of it fell back immediately, but some of it remained as dust in the atmosphere for months. This material, along with the smoke from the fires, shrouded Earth, creating a form of nuclear winter. 可知A选项正确，太阳被地球大气的灰尘和烟挡住了。
13. Look at the four squares [■] that indicate where the following sentence could be added to the passage. 【句子插入题】
Some explanations seem plausible until the facts are considered.
Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.
Dinosaurs rapidly became extinct about 65 million years ago as part of a mass extinction known as the K-T event, because it is associated with a geological signature known as the K-T boundary, usually a thin band of sedimentation found in various parts of the world (K is the traditional abbreviation for the Cretaceous, derived from the German name Kreidezeit). [■] Many explanations have been proposed for why dinosaurs became extinct. [■] For example, some have blamed dinosaur extinction on the development of flowering plants, which were supposedly more difficult to digest and could have caused constipation or indigestion—except that flowering plants first evolved in the Early Cretaceous, about 60 million years before the dinosaurs died out. [■]In fact, several scientists have suggested that the duckbill dinosaurs and homed dinosaurs, with their complex battery of grinding teeth, evolved to exploit this new resource of rapidly growing flowering plants. [■]Others have blamed extinction on competition from the mammals, which allegedly ate all the dinosaur eggs—except that mammals and dinosaurs appeared at the same time in the Late Triassic, about 190 million years ago, and there is no reason to believe that mammals suddenly acquired a taste for dinosaur eggs after 120 million years of coexistence Some explanations (such as the one stating that dinosaurs all died of diseases) fail because there is no way to scientifically test them, and they cannot move beyond the realm of speculation and guesswork.
答案：A
解析：根据待插入句子前的一句话Many explanations have been proposed for why dinosaurs became extinct.已经提出了很多关于为什么恐龙会灭绝的解释。待插入句子意为，有些解释直到一些事实被考虑之后看起来才可信，符合语境。所以A选项正确。
14. Direction: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
【概要小结题】
Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it.
To review the passage, click VIEW TEXT.
Over the years, scientists have proposed a number of theories as to why dinosaurs suddenly became extinct about 65 million years ago.
Answer Choices
A. Many explanations for dinosaur extinction have been proposed, but most of them are either called into question by known facts or are merely unsupported hypotheses.
B. Focusing on dinosaurs misses the point that the extinction, at about the same time, of the shelled squidlike creatures that dominated the Mesozoic seas was far more scientifically significant.
C. Computerized climate models of global temperature fluctuations support the theory that a huge rock from space hit the Yucatan Peninsula in Mexico about 65 million years ago.
D. Although mammals and dinosaurs appeared at about the same time in the Late Triassic, the K-T event, which marked the end of the dinosaurs, apparently had relatively little impact on mammals.
E. Any satisfactory explanation of the mass extinction of dinosaurs must take into account the fact that the disappearance of the dinosaurs was part of a global mass extinction.
F. A huge bolide striking Earth would have created conditions in which most plants would have died, thus explaining the mass extinction of organisms—including dinosaurs—further up the food chain.
答案：A, E, F
解析：
全文都在对恐龙的灭绝进行解释，一些是据已知事实而被质疑的，一些是没有理论依据支持的，所以A选项正确。
根据原文These included a variety of clams and snails, and especially the ammonites, a group of shelled squidlike creatures that dominated the Mesozoic seas and had survived many previous mass extinctions.文中并没有提及无贼占据中生代海域是否更加重要，所以B选项错误。
根据computerized climate models 定位至原文According to computerized climate models, global temperatures fell to near the freezing point, photosynthesis halted, and most plants on land and in the sea died.发现文中并未提及computerized climate models是否可以支持火流星坠落的理论。所以C选项错误。
根据mammals 定位至except that mammals and dinosaurs appeared at the same time in the Late Triassic, about 190 million years ago, and there is no reason to believe that mammals suddenly acquired a taste for dinosaur eggs after 120 million years of coexistence Some explanations (such as the one stating that dinosaurs all died of diseases) fail because there is no way to scientifically test them, and they cannot move beyond the realm of speculation and guesswork.发现文中并未提及对于哺乳动物的影响，所以D选项错误。
根据global定位至原文By contrast, any explanation that focuses strictly on the dinosaurs completely misses the point The Cretaceous extinctions were a global phenomenon, and dinosaurs were just a part of a bigger picture.所以E选项正确。
根据原文The impact displaced huge volumes of seawater, causing much flood damage in the Caribbean. Meanwhile, the bolide itself excavated 100 cubic kilometers of rock and debris from the site, which rose to an altitude of 100 kilometers. Most of it fell back immediately, but some of it remained as dust in the atmosphere for months. This material, along with the smoke from the fires, shrouded Earth, creating a form of nuclear winter.可知，火流星撞击地球创造了大多数植物会灭亡的条件，所以F选项正确。
以上的内容就是托福tpo42阅读题目及答案解析：Explaining Dinosaur Extinction，希望可以对你们备考有一定帮助。