2019年8月24日托福阅读真题+题目+答案：The Eocene Hothouse

2019年8月24日托福阅读真题+题目+答案：The Eocene Hothouse

The world of the Cretaceous period (144-65 million years ago), the time of the dinosaurs, was a greenhouse world with high temperatures, perhaps caused by elevated levels of carbon dioxide. ■The early Eocene (56-34 million years ago), which followed the Paleocene (65-56 million years ago), was even hotter. ■Some models of carbon dioxide values place the early Eocene atmospheric level at around 1,000 parts per million, about three times the present level but less than half of the level at the warmest greenhouse conditions of the Cretaceous. ■Some geologists also see high carbon dioxide levels as the main factor for these greenhouse conditions. ■But some paleobotanists have looked at the stomata, the tiny pores found on the undersides of leaves that plants use to exchange oxygen and carbon dioxide with the outside atmosphere. During conditions of high carbon dioxide, plants make fewer stomata because they can get carbon dioxide for photosynthesis much more easily and lose less water in the process. Conversely, low carbon dioxide conditions trigger leaf growth with more stomata. The biologist Dana Royer and colleagues found that the stomatal density on living fossils such as the dawn redwood metasequoia and gingko has been fairly constant since the end of the Cretaceous, which suggests that the carbon dioxide level was not that much higher in the early Eocene than it is today. Greg Retallack looked at plant cuticles and found that the carbon dioxide level was only slightly higher than modern levels. Other researchers have demonstrated that the carbon dioxide balance and acidity in the world's oceans were consistent with an atmospheric carbon dioxide level only slightly higher than the level we have today.

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1.According to paragraph 1, one effect of an increase in carbon dioxide levels is that

A the process of photosynthesis slows down

B plant leaves need fewer stomata

C leaf stomata are closer together

D plants need less water

2.In paragraph 1, why does the author include the discussion about paleobotanists' study of stomata?

A To describe the effects of carbon dioxide on living fossils

B To explain why some scientists question whether atmospheric carbon levels in the early Eocene were about 1,000 parts per million

C To explain how photosynthesis in plants has been affected by changing amounts of carbon dioxide in the atmosphere

D To explain why a high exposure to carbon dioxide is an advantage for plant growth

3.In paragraph 1, the information from studies of carbon dioxide values supports which of the following conclusions?

A Carbon dioxide levels have little effect on the stomatal density of living fossils.

B Carbon dioxide levels altered the ocean's acidity before the levels changed in the atmosphere.

C Carbon dioxide levels of the early Eocene were overestimated.

D Carbon dioxide levels of the warmest part of the Cretaceous were overestimated.

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2019年8月24日托福阅读真题+题目+答案：The Eocene Hothouse，完整版下载，10元有偿！