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  3. About ten men in every hundred suffer from colour blindness in some way; women are luckier only about one in two hundred is affe

About ten men in every hundred suffer from colour blindness in some way; women are luckier only about one in two hundred is affe

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问题    About ten men in every hundred suffer from colour blindness in some way; women are luckier only about one in two hundred is affected in this manner. There are different forms of colour blindness. A man may not be able to see deep red. He may think that red, orange and yellow are all shades of green. Sometimes a person cannot tell the differenee between blue and green. In rare cases an unlucky man may see everything in shades of green—a strange world indeed.
   In certain occupations colour blindness can be dangerous and candidates are tested most carefully. For example, when fighting at night, soldiers use lights of flares to signal to each other. A green light may mean "Advance" and a red hght may mean "Danger! Keep back!" You can see what will happen if somebody thinks that red is green! Colour blindness in human’ beings is a strange thing to explain. In a single eye there are millions of very small things called "cones". These help to see in a bright light and to tell the difference between colours. There are also millions of "rods" but these are used for seeing when it is nearly dark. They show us shape but not colour. Wait until it is dark tonight, then go outside. Look round you and try to see what colors you can recognize.
   Birds and animals which hunt at night have eyes which contain few or no cones at all, so they cannot see colours. As far as we know, bats and adult owls cannot see colours at all. Similarly cats and dogs cannot see colours as well as we can. Insects can see ultraviolet rays which are invisible to us, and some of them can even see X-rays. The wings of a moth may seem grey and dull to us, but to insects they may appear beautiful, showing colours which we cannot see. Scientists know that there are other colours around us which insects can see but which we cannot see. Some insects have favorite colours. Mosquitoes like blue, but do not like yellow. A red light will not attract insects but a blue tamp will.
When millions of rods in our eyes are at work in darkness we call see
选项 A、colours only
B、shapes and colours
C、shapes only
D、darkness only
答案C
解析 这道细节题可以用“rods"这个专业词汇帮助我们在第二段中迅速定位，在这里，作者告诉我们视杆细胞(rod)在天色接近黑暗时发挥作用，他们能使我们看到物体的外形，而不是颜色。故选C。
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