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该题平均耗时:2m8s,平均正确率:72.5% 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.

The passage presents which of the following facts as evidence that tends to undermine 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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当前版本由 01**** 更新于2016-01-24 16:06:06 感谢由 01**** 对此题目的解答所做出的贡献。

注意题目问的是:facts as evidence 作为发驳A理论的事实证据;

第一段讲arboreal 理论的缺点是重点。总共分了四个分论点论述。在阅读平行论述的细节时,如何判断考点比较容易出在哪里?就要有敏感来找区别。这里如果读的熟练的话,除了第二个,其他三个都是推理式结论,或者是反面论述结论,即“它没有……”。而题目问的是evidence,是事实,所以只有第二个是“化石结果证明no plants taller”,一对照题目削弱arboreal理论,就知道是D了。

C选项:small animal的例子在括号里是对第三个缺点起解释作用,说他们能爬树,但是不能滑行。这只是evidence of "Even if the animals could climb trees, this ability is not (35) synonymous with gliding ability."

并不是evidence of “that tends to undermine the arboreal hypothesis? ” 削弱范围太小了~~

而E:“跳跃到空中并不能足以证明从树上滑行时有足够的加速度。”acceleration问题是cursorial理论反驳a理论的观点。不是fact而是推导。

因此可以看到:题干问Fact as evidence 就一定是严谨的文中有照应的句子。作者的推导式结论都不足以说明是fact.只有fossil才够格



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    bella

    其他选项容易排除,难点在于C和D的选择
    
    虽然CD原文都有提到,C错在,这是一个不完整的驳斥evidence,原文用来驳斥arboreal的evidence是Many small animals, and even some goats and kangaroos, are capable of climbing trees but are not gliders.即小动物会爬树但不一定会glibing这个完整句,只说小动物会爬树不仅是个不完整的例子,反而还支持arboreal假说,而D答案就很完整,原文说到没有足够高的树,选D
    0 0 回复 2015-11-24 10:10:53
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