托福阅读常考话题及练习题推荐五：恐龙大灭绝（2）

1 托福阅读常考话题：恐龙大灭绝练习题

Paragraph 1: It was not until the Cambrian period, beginning about 600 million years ago, that a great proliferation of macroscopic species occurred on Earth and produced a fossil record that allows us to track the rise and fall of biodiversity. Since the Cambrian period, biodiversity has generally risen, but there have been some notable exceptions. Biodiversity collapsed dramatically during at least five periods because of mass extinctions around the globe. The five major mass extinctions receive most of the attention, but they are only one end of a spectrum of extinction events. Collectively, more species went extinct during smaller events that were less dramatic but more frequent. The best known of the five major extinction events, the one that saw the demise of the dinosaurs, is the Cretaceous-Tertiary extinction.

1. The word “proliferation” in the passage is closest in meaning to

A. decline

B. extinction

C. increase

D. migration

2. Paragraph 1 supports which of the following statements about life on Earth before the Cambrian period?

A. Biodiversity levels were steady, as indicated by the fossil record.

B. Levels of biodiversity could not be tracked.

C. The most dramatic extinction episode occurred.

D. Few microscopic species existed.

Paragraph 2: Starting about 280 million years ago, reptiles were the dominant large animals in terrestrial environments. In popular language this was the era “when dinosaurs ruled Earth,” when a wide variety of reptile species occupying many ecological niches. However, no group or species can maintain its dominance indefinitely, and when, after over 200 million years, the age of dinosaurs came to a dramatic end about 65 million years ago, mammals began to flourish, evolving from relatively few types of small terrestrial animals into the myriad of diverse species, including bats and whales, that we know today. Paleontologists label this point in Earth’s history as the end of the Cretaceous period and the beginning of the Tertiary period, often abbreviated as the K-T boundary. This time was also marked by changes in many other types of organisms. Overall, about 38 percent of the families of marine animals were lost, with percentages much higher in some groups Ammonoid mollusks went from being very diverse and abundant to being extinct. An extremely abundant set of planktonic marine animals called foraminifera largely disappeared, although they rebounded later. Among plants, the K-T boundary saw a sharp but brief rise in the abundance of primitive vascular plants such as ferns, club mosses, horsetails, and conifers and other gymnosperms. The number of flowering plants (angiosperms) was reduced at this time, but they then began to increase dramatically.

3. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

A. The dominance of dinosaurs came to an end 65 million years ago, at which time mammals began to flourish and diversify.

B. Because no group of species can remain dominant forever, mammals became the dominant group when dinosaurs became extinct.

C. After being the dominant group for more than 200 million years, the age of dinosaurs came to a dramatic end 65 million years ago.

D. The diverse group of mammals that we know today, including bats and whales, evolved from small terrestrial forms that had been dominated by dinosaurs.

4. According to paragraph 2, why are dinosaurs popularly said to have “ruled Earth” during the Cretaceous period?

A. Dinosaurs were the only species of reptile that existed during the whole of the Cretaceous period.

B. Dinosaurs won the battle for food resources over mammals during the Cretaceous period.

C. Dinosaurs survived extinction during the Cretaceous period, whereas many other animal species did not.

D. Dinosaurs were the physically and ecologically dominant animals during the Cretaceous period.

5. According to paragraph 2, which of the following species initially increased in number at the K-T boundary?

A. Dinosaurs

B. Foraminifera

C. Ferns

D. Ammonoid mollusks

Paragraph 3: What caused these changes? For many years scientists assumed that a cooling of the climate was responsible, with dinosaurs being particularly vulnerable because, like modern reptiles, they were ectothermic (dependent on environmental heat, or cold-blooded). It is now widely believed that at least some species of dinosaurs had a metabolic rate high enough for them to be endotherms (animals that maintain a relatively consistent body temperature by generating heat internally). Nevertheless, climatic explanations for the K-T extinction are not really challenged by the ideas that dinosaurs may have been endothermic, because even endotherms can be affected by a significant change in the climate.

6. Why does the author note that “even endotherms can be affected by a significant change in the climate”?

A. To argue that there was a significant climate at the time that endothermic dinosaurs became extinct

B. To argue that climate change caused some dinosaurs to evolve as endotherms

C. To support the view that at least some of the dinosaurs that became extinct were endotherms

D. To defend climate change as possible explanation for the extinction of dinosaurs