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暑假六级阅读训练23

2014-08-13    来源:网络    【      托福雅思口语高分过

The human criterion for perfect vision is 20/20 for reading the standard lines on a Snellen eye chart without a hitch. The score is determined by how well you read lines of letters of different sizes from 20 feet away. But being able to read the bottom line on the eye chart does not approximate perfection as far as other species are concerned. Most birds would consider us very visually handicapped. The hawk. for instance, has such sharp eyes that it can spot a dime on the sidewalk while perched on top of the Empire State Building+ It can make fine visual distinctions because it is blessed with one million cones per square millimeter in its retina(视网膜). And in water, humans are farsighted. while the kingfisher, swooping down to spear fish. can see well in both the air and water because it is endowed with two foveae.(凹窝)-areas of the eye, consisting mostly of cones. that provide visual distinctions. One fovea permits the bird, while in the air. to scan the water below with one eye at a time. This is called monocular vision. Once it hits the water, the other fovea joins in, allowing the kingfisher to focus both eyes, like binoculars, on its prey at the same time. A frog's vision is distinguished by its ability to perceive things as a constant motion picture. Known as "bug detectors", a highly developed set of cells in a frog's eyes responds mainly to moving objects. So, it is said that a frog sitting in a field of dead bugs wouldn’t see them as food and would starve.

The bee has a "compound" eye. which is used for navigation. It has 15,000 facets that divide what it sees into a pattern of dots. or mosaic. With this hind of vision, the bee sees the sun only as a single dot, a constant point of reference. Thus. the eye is a superb navigational instrument that constantly measures the angle of its line of flight in relation to the sun. A bee's eye also gauges flight speed. And if that is not enough to leave our 20/20 "perfect vision” paling into insignificance. the bee is capable of seeing something we can't-ultraviolet light. Thus,what humans consider to be "perfect vision” is in fact rather limited when we look at other species. However, there is still much to be said for the human eye. Of all the mammals, only humans and some primates can enjoy the pleasures of color vision.

【参考译文】
判断人的视力是否完好的标准是看他是否在看Snellen视力表的时候能毫无障碍地达到20/20的视力。[1]测试值取决于从20英尺之外,你能看到多少行大小不一的字母。但是,即使我们能看到视力表的最底一行,和别的物种相比,那也不意味着拥有完美的视力。大多数的鸟类可能觉得我们在视力上都有缺陷。[2]例如,鹰的视力非常锐利,当它盘踞在帝国大厦的楼顶时,它能看清在人行道上的一角硬币。它有如此好的视觉分辨能力,是因为它的视网膜上每平方毫米就有100万个圆锥细胞。在水中,人类是远视的;相比之下,俯冲到水里捉鱼的翠鸟在水上和水下都能看清景物,因为它的眼睛里有两个凹窝区域,这两个凹窝主要由具有视觉分辨能力的圆锥细胞组成。[3]其中一个凹窝让飞翔在空中的翠鸟不时用一只眼瞳扫视水面的情况——这被称为单眼视觉。翠鸟一旦扎入水中,另一个凹窝也发挥功能,使它的双眼像双筒望远镜一样同时聚焦到猎物身上。青蛙的视力特点是它能感知像移动画面那样的物体。青蛙被称为“昆虫探测器”,在它的眼睛里有一组高度发达的细胞,主要能够对移动的物体产生反应。所以,据说,如果青蛙坐在一片虫子的尸体旁,它看不到那些可以作为食物的虫干,最终会被饿死。

蜜蜂的眼睛是复眼,用于导航。它的眼睛有15000个面,把它看到的物体分割为马赛克式的小点。[4]有了这种视觉特点,蜜蜂看到的太阳只是一个小点,一个不变的参照点。所以,它的眼睛是一个极好的导航仪器,能不断地量度飞行的线路与太阳的角度。蜜蜂的眼睛还能测量飞行的速度。如果这样还不能让我们人类20/20的完美视力显得微不足道的话,蜜蜂还能看到紫外线,这是我们人类无法看到的。因此,当我们与别的特种相比时,人类认为“完美的视力”实际上很有局限性的。然而,对于人类的眼睛还是有很多可以称赞的:在所有哺乳动物当中,只有人类和某些灵长类动物能享受分辨颜色的喜悦。

【测试题】
1. The Snellen eye chart measures one's eyesight by__________________.
A) the number of lines he reads
B) the distance he stands away from the chart
C) the speed at which he recognizes the letters
D) several integrative factors

2. How is hawk's eyesight better than ours?
A) It can identify small items more quickly than we do.
B) It can see ai a longer distance than we do.
C) It has more cones in che retina than we do.
D) It has bigger eyes than we do.

3. Monocular vision enables the kingfisher to__________________.
A) avoid farsightedness             B) be able to see underwater
C) move one eye at a time          D) focus its eyes on the prey

4. A bee finds its direction by_______________________.
A) dividing what it sees into thousands of dots
B) constantly gauging its flying speed
C) using the sun as a constant point of reference
D) measuring the angle of the sun

5. What is the main idea of the passage'?
A) The differences between human eyes and other species' eyes.
B) The advantages of other species' eyes in comparison with human eyes.
C) The factors that make other species' eyes better than human eyes.
D) The standard that determines me "perfect vision” of human eyes.
 



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