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  3. Nature has devised many ways to protect creatures’ eyes. The most common protection is the eyelid--a fold of skin that closes ov

Nature has devised many ways to protect creatures’ eyes. The most common protection is the eyelid--a fold of skin that closes ov

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问题     Nature has devised many ways to protect creatures’ eyes. The most common protection is the eyelid--a fold of skin that closes over the eye, protecting it from damage. Eyelashes are useful for keeping out dust and other irritants, and tears wash away any particles that get through the other defenses.
    Some creatures, including most birds, have three eyelids. The upper and lower lids act like human lids and keep out twigs, dirt and sand. The third eyelid, however, is a semitransparent tissue that crosses over the eye from the inside corner to the outside corner. Because of this protective membrane, birds seldom have to blink. They close their eyes only when they go to sleep. In ducks, this third eyelid self as an underwater diving mask that helps the ducks find food.
    Most fish and snakes have no eyelids at all. Instead, a hard glassy covering protects their eyes. In fish, water constantly sweeps away dirt from the covering. And a snake’s eyesight is usually so bad that a little dirt obscuring its vision does not disturb it greatly.
    Eyelashes defend the eye by shading it from glare. They also act like miniature brushes to remove dust. Camels have lashes that are four inches long to protect their eyes from windblown sand in the desert.  
The writer implies that eyelids are ______.
选项 A、not found on lizards
B、nice to look at
C、always covered with eyelashes
D、the most effective eye protection
答案D
解析 作者说，大多数的鱼和蛇没有眼皮，但并未说所有的蜥蜴都没有眼皮，排除选项A。第一段说眼皮和眼睫毛都是保护眼睛的；第二段说有些动物如鸟类有三层眼皮，但并未说睫毛；第三段说有些动物没有眼皮；第四段说骆驼的睫毛长。这些都未提及有眼皮就肯定有睫毛，排除选项C。选项D是正确的。
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