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该题平均耗时:2m55s,平均正确率:61.7% 添加做题笔记

Two opposing scenarios, the “arboreal” hypothesis and the “cursorial” hypothesis, have traditionally been put forward concerning the origins of bird flight. The “arboreal” hypothesis holds that bird ancestors began to fly by climbing trees and gliding down from branches with the help of incipient feathers: the height of trees provides a good starting place for launching flight, especially through gliding. As feathers became larger over time, flapping flight evolved and birds finally became fully air-borne. This hypothesis makes intuitive sense, but certain aspects are troubling. Archaeopteryx (the earliest known bird) and its maniraptoran dinosaur cousins have no obviously arboreal adaptations, such as feet fully adapted for perching. Perhaps some of them could climb trees, but no convincing analysis has demonstrated how Archaeopteryx would have both climbed and flown with its forelimbs, and there were no plants taller than a few meters in the environments where Archaeopteryx fossils have been found. Even if the animals could climb trees, this ability is not synonymous with gliding ability. (Many small animals, and even some goats and kangaroos, are capable of climbing trees but are not gliders.) Besides, Archaeopteryx shows no obvious features of gliders, such as a broad membrane connecting forelimbs and hind limbs.

The “cursorial”(running) hypothesis holds that small dinosaurs ran along the ground and stretched out their arms for balance as they leaped into the air after insect prey or, perhaps, to avoid predators. Even rudimentary feathers on forelimbs could have expanded the arm’s surface area to enhance lift slightly. Larger feathers could have increased lift incrementally, until sustained flight was gradually achieved. Of course, a leap into the air does not provide the acceleration produced by dropping out of a tree; an animal would have to run quite fast to take off. Still, some small terrestrial animals can achieve high speeds. The cursorial hypothesis is strengthened by the fact that the immediate theropod dinosaur ancestors of birds were terrestrial, and they had the traits needed for high lift off speeds: they were small, agile, lightly built, long-legged, and good runners. And because they were bipedal, their arms were free to evolve flapping flight, which cannot be said for other reptiles of their time.

Which of the following is included in the discussion of the cursorial hypothesis but not in the discussion of the arboreal hypothesis?


  • 分析A选项
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  • 分析B选项
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  • 分析C选项
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  • 分析D选项
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  • 分析E选项
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暂无雷哥网文字解析
当前版本由 bella 更新于2015-11-24 10:14:49 感谢由 bella 对此题目的解答所做出的贡献。

看清题目,只在C假说里提到,但是A假说里没有的,选C,原文最后写了because they were bipedal,给出了一个理由


a中的Ar鸟,是A假说的

b同a

d滑翔能力,都涉及到了

e需要花的时间,都没有提到


题目讨论 3条评论)

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  • 用户头像
    Smellycatt

    E错的原因是 只在arboreal提到了 没有在c提到... 注意审题...
    0 0 回复 2020-08-05 16:58:16
  • 用户头像
    Aaronlee

    C
    第二段第一句中 ...as they leaped into the air after insect prey or, perhaps, to avoid predators讲了第二个假设起跑飞的原因,第一个假设中没有提为什么要上树飞
    0 0 回复 2020-07-17 18:20:47
  • 用户头像
    Hixon

    出这种题还有人性吗?要花多少时间把这么长两段看完还仔细来对比
    0 0 回复 2019-05-09 00:57:18
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