2019年12月大学英语六级第一套真题及答案-2019年12月大学英语六级阅读晨读美文：Vision

【#四六级考试# 导语】英语四六级考试将要在2019年12月进行，日常的备考，听说读写都要关注，其中阅读理解是考生复习的重点和难点，日常备考需要加强英文阅读练习，下面是®文档大全网四六级频道为大家整理的《2019年12月大学英语六级阅读晨读美文：Vision》一文，希望给大家带来帮助。

Vision

　　Human vision like that of other primates has evolved in an arboreal environment. In the dense complex world of a tropical forest, it is more important to see well than to develop an acute sense of smell. In the course of evolution members of the primate line have acquired large eyes while the snout has shrunk to give the eye an unimpeded view. Of mammals only humans and some primates enjoy color vision. The red flag is black to the bull. Horses live in a monochrome world. Light visible to human eyes however occupies only a very narrow band in the whole electromagnetic spectrum. Ultraviolet rays are invisible to humans though ants and honeybees are sensitive to them. Humans have no direct perception of infrared rays unlike the rattlesnake which has receptors tuned into wavelengths longer than 0.7 micron. The world would look eerily different if human eyes were sensitive to infrared radiation. Then instead of the darkness of night, we would be able to move easily in a strange shadowless world where objects glowed with varying degrees of intensity. But human eyes excel in other ways. They are in fact remarkably discerning in color gradation. The color sensitivity of normal human vision is rarely surpassed even by sophisticated technical devices.

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