托福阅读生物类真题.docx

1、托福阅读生物类真题托福阅读生物类真题小编又带来托福资料了，今天给大家带来的是托福资料之托福阅读生物类真题，文章里面是介绍关于生物方面的问题，大家可以感受一下生物类文章的套路，然后后面有问题提问，并且后面附有答案哦，希望可以帮助大家，下面我们就一起来看看吧。Title：The Extinction of the DinosaursGeologists define the boundary between sediment layers of the Cretaceous period (144. C65 million years ago) and the Paleocene period (

2、65. C55 million years ago) in part by the types and amounts of rocks and fossils they contain or lack.Before the limit of 65 million years ago, marine strata are rich in calcium carbonate due to accumulations of fossils of microscopic algae deposited on the sea floor. Above the 65-million-year limit

3、, sea-floor sediments contain much less calcium carbonate, and fossils of several families of mollusks are no longer found. In continental sediments, dinosaur fossils, though frequent before 65 million years ago, are totally absent.By contrast, new families of mammals appear, including large mammals

4、 for the first time. Scientists wondered for many years about what could have caused the dinosaurs rapid disappearance at the end of the Cretaceous period, coming up with a great variety of theories and scenarios. For some, it could have been due to unfavorable genetic changes triggered by a dramati

5、c increase by a factor of 10, 100, 1, 000 in cosmic-ray particles reaching the Earth after a supernova explosion somewhere in the neighborhood of the solar system. For these high-energy particles to affect life, they would have to get through the protective barrier of the Earths magnetosphere, the r

6、egion of the upper atmosphere controlled by Earths magnetic field. That could have happened if the cloud of particles from the supernova explosion reached the Earth during a period when the magnetosphere was weakened, something that may happen when the Earths magnetic field changes direction. And we

7、 know that the magnetic north and south poles of the Earth switch on the average twice every million years. However, this is not the only possible explanation for dinosaur destruction.Other theories have raised the possibility of strong climate changes in the tropics (but they then must be explained

8、). Certainly, if climate changes, the changed distributions of temperature and rainfall modify the conditions that favor one ecosystem over another. The extinction of a particular family, genus, or species may result from a complicated chain of indirect causes and effects. Over thirty years ago, sci

9、entist Carl Sagan quoted one suggestion that the demise of the dinosaurs resulted from the disappearance of a species of fern plant that was important for dinosaur digestion. Other theories involved a worldwide cold wave following the spread of a layer of cold but not very salty water in the worlds

10、oceans, which floated on the surface because, with its low salinity, the water was less dense.Proponents of another theory that remains under consideration today postulate that the extinction of the dinosaurs corresponds to a period of intense volcanic activity. Its not a question of just one or eve

11、n of a thousand eruptions comparable to the explosion of Krakatoa in 1883, one of the largest volcanic events in modern times, but rather of a prolonged period of activity. On the Deccan plateau in India, basalt (volcanic) rocks cover more than 500, 000 square kilometers (nearly 200, 000 square mile

12、s), and correspond to massive lava outflows occurring precisely at the end of the Cretaceous. This sort of outflow could correspond to volcanic activity similar to the activity that drives sea-floor spreading, with lava emerging from elongated fractures in the crust rather than from craters.The volc

13、anic convulsion that buried the Deccan plateau in lava must also have changed the composition of the atmosphere and severely affected climate. Initially, there must have been strong sudden cooling resulting from the blocking of sunlight by sulfate aerosol veils in the stratosphere (part of the Earth

14、s atmosphere). If strong cooling lasted a year after the formation of the aerosols, it would have been the death of tropical species unable to adapt to such a volcanic winter.However, a long period of strong volcanic activity (again, remember thousands of Krakatoas) would at the same time have added

15、 a substantial amount of carbon dioxide to the atmosphere, reinforcing the greenhouse effect. This would gradually warm things up, ending the extended cold snap and producing global warming together with geographic shifts of humid and arid (dry) zones. Certainly things would change to upset living c

16、onditions, leading to the extinction of some species while others would profit, if only from the disappearance of predators.1. According to paragraph 1, which of the following is true of Paleocene sedimentsA. They lack fossils from some families of mammals found in Cretaceous sediments.B. They conta

17、in fossils of dinosaurs.C. They contain fossils of some animals that did not exist during the Cretaceous.D. They contain fossils of more kinds of mollusks than are found in Cretaceous sediments.2. The word unfavorable in the passage is closest in meaning toA. UnusualB. DisadvantageousC. SuddenD. maj

18、or3. The word triggered in the passage is closest in meaning toA. initiatedB. intensifiedC. followedD. aided4. Why does the author include the information that the magnetic north and south poles of the Earth switch on the average twice every million yearsA. To provide evidence showing that Earths pr

19、otective barrier is difficult to get throughB. To show that it is reasonable to think that particles from a supernova explosion could have reached EarthC. To explain why some scientists believe a supernova explosion may have occurred near our solar systemD. To help explain why some scientists have r

20、ejected the theory presented in paragraph 25. According to the theory discussed in paragraph 2，a weakening of Earths magnetosphere may haveA. caused a supernova to explode near our solar systemB. allowed gene-altering particles to reach Earths surfaceC. forced Earths magnetic field to change directi

21、onD. allowed clouds of protective particles to escape from Earths upper atmosphere6. AII of the following are mentioned in paragraph 3 as possible causes for the extinction of the dinosaurs EXCEPTA. a change in the diet of dinosaursB. a change in the climate of the tropicsC. a decrease in global tem

22、peraturesD. a decrease in deep ocean salinity7. In paragraph 3，why does the author include the quotation by Carl SaganA. To explain the connection between dinosaur extinction and the extinction of other animal speciesB. To support the claim about species extinction being due to indirect causes and e

23、ffectsC. To show that scientists have revised their ideas greatly in the last thirty yearsD. To identify the differences between the various theories for the extinction of dinosaurs8. According to paragraph 4，what was one unusual aspect of the volcanic activity at the end of the CretaceousA. Some ex

24、plosions were much larger than Krakatoa.B. Eruptions occurred over a long period of time.C. Active volcanoes were sometimes separated by many kilometers.D. There were active volcanoes in the sea as well as on land.9. Which of the following is presented in paragraph 4 as evidence that intense volcani

25、c activity occurred at about the time that the dinosaurs became extinctA. The size of the volcanic craters on the Deccan plateauB. An increase in sea-floor spreadingC. The formation in India of large amounts of a type of rock associated with volcanoesD. The occurrence of a thousand or more volcanic

26、explosions the size of Krakatoa10. The word severely in the passage is closest in meaning toA. certainlyB. consequentlyC. greatlyD. permanently11. The word reinforcing in the passage is closest in meaning toA. making possibleB. spreadingC. introducingD. strengthening12. According to paragraph 5，all

27、of the following are theorized to have occurred as a result of volcanic activity EXCEPTA. a decrease in the amount of sunlight reaching Earths surfaceB. a reduction in the number of sulfate aerosol veils in the stratosphereC. increased dryness in some areas that were once more humidD. changes in the

28、 atmospheres composition resulting in an increase in temperature13. Look at the four squares that indicate where the following sentence could be added to the passage.Thus, ecosystems following periods of extensive volcanic activity necessarily had different combinations of species than earlier ecosy

29、stems did.Where would the sentence best fit Click on a square to add the sentence to the passage.(题目不完整)14. Drag your choices to the spaces where they belong. To review the passage, click on View TextAnswer ChoicesA. Cosmic rays from a nearby supernova explosion may have penetrated Earths atmosphere

30、, causing genetic changes that dinosaur populations could not survive.B. Climate changes in the tropics may have set off a chain of indirect effects that negatively affected the ecosystems in which dinosaurs lived.C. The spread of lava over large part s of previously favored habitats such as the Dec

31、can Plateau may have made these favored areas uninhabitable for many years.D. Although the volcanic winter resulting from the formation of sulfate aerosols eventually ended, temperatures may have remained below levels required by dinosaurs to survive.E. Temperature changes and geographic shifts in climate zones due to the atmospheric effects of volcanic activity may have been significant enough to cause extinction.F. To be convincing ，theories about what caused dinosaurs to become extinct must be able to explain the disappearance of other predators in the food chain at the same time