题目内容：
根据以下材料回答第 1～4 题：Nature has devised many ways to protect creatures’eyes．The most commoll protection is t he eyelid--a fold of skin that closes over the eye，protecting it form 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 Iike human lids and keep out twigs，dirt and sand．The third eyelid，however，is a semitransparent tissue that crosses over the eye from the insied corner to the outside corher．Because of this protective membrane，birds seldom have to blink．They close theireyes only when they go to sleep．In ducks，this third eyelid self as an underwater divingmask 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 sway dirt from the covering．And a snake’s eyesight is usuallyso 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 bru-shes to remove dust．Camels have lashes that are four inches long to protect their eyesfrom windblown sand in the desert．
A camel has long eyelashes ．
参考答案：
答案解析：