2018年12月英语六级听力音频-2018年12月英语六级听力常考时文：EvolutionandWheels

【#四六级考试# 导语】英语听力是英语四六级考试中的重要组成部分，对于中国的考生，日常英文听说机会少，缺少听力训练，所以在备考大学英语四六级时，需要加强听力的训练。针对这一情况，©文档大全网英语四六级频道特别整理听力相关文章《2018年12月英语六级听力常考时文：Evolution and Wheels》，供学员参考使用。预祝大家高分通过考试。

　2018年12月大学英语六级听力常考时文盘点

　　英语六级听力常考时文：Evolution and Wheels

　　1.What connects the living cells to the heart in an animal's body? ...

　　2.What is crucial to a wheel? ...

　　3.What is the feature of cats' claws? ...

　　In the past, evolutionary biologists contemplating the absence of wheels in nature agreed that the explanation was not undesirability: wheels would be good for animals, just as they are for us. Animals were prevented from evolving wheels, the biologists reasoned, by the following dilemma: living cells in an animal's body are connected to the heart by blood vessels, and to the brain by nerves. Because a rotating joint is essential to a wheel, a wheel made of living cells would twist its artery vein and nerve connections at the first revolution, making living impracticable. However, there is a flaw in the argument that the evolution of wheeled animals was thwarted by the insoluble joint problem. The theory fails to explain why animals have not evolved wheels of dead tissue with no need for arteries and nerves. Countless animals, including us, bear external structures without blood supply or nerves - for example, our hair and fingernails, or the scales, claws, and ho rns of other animals. Why have rats not evolved bony wheels, similar to roller skates? Paws might be more useful than wheels in some situations, but cats' claws are retractable: why not retractable wheels? We thus arrive at the serious biological paradox flippantly termed the RRR dilemma: nature's failure to produce rats with retractable roller skates.

　　2018年12月大学英语六级听力常考时文盘点

2018年12月英语六级听力常考时文：Evolution and Wheels.doc

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