Some snakes eat other snakes, even poisonous ones. The poison does not do them any harm(伤害). Snakes can swallow(吞下) things that are bigger around than they themselves are. This is possible because the jawbones(腭骨) are loosely joined, and the mouth can stretch（伸展）to make room for a fat animal. The snake’s slim body stretches to make space for the animal when it is inside.
Many snakes eat birds’ eggs or frogs（青蛙）. Others eat pests（害虫）, mice and other animals that harm crops on farms. Because snakes do this valuable work, you should never kill one. It is too dangerous for you to kill a poisonous one. Leave that job to experts.
【小题1】 Which of the following groups of food is usually had by a snake?A．Mice, crops, birds’ eggs.B．Pests, frogs, some animals, plants.C．Birds’ eggs, frogs, all animals, other snakes. D．Mice, frogs, pests, some animals, other snakes.【小题2】We should not kill a snake because A．it is poisonousB．it can do something useful for manC．it will strike you in returnD．we are not experts【小题3】Snakes may do some valuable work by A．eating pests, mice and some harmful animalsB．doing harm to other animalsC．eating birds’ eggs and frogsD．both A and C【小题4】In writing this passage the writer mainly wants us to A．have a better impression(印象) about snakesB．like snakesC．kill snakes with the help of expertsD．regard snakes as one of man’s best friendsD
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(答案→)D
解析：提到蛇你会想到什么？有毒、可怕或者会伤人？其实蛇的食物链有很多，包括蛇、青蛙鸟蛋，更有老鼠等破坏庄稼的动物。从这一点来看，对人类还是有益的。它的攻击大多是出于自卫和猎食。那就顺其自然吧。
【小题1】细节理解题。根据第二段可知，蛇吃其他的蛇、鸟蛋、青蛙、还吃害虫、破坏庄稼的老鼠和其他动物，但是不吃庄稼和植物，也不是所有的动物都吃，所以排除其他选项， 选D。
【小题2】细节理解题。根据第二段可知，尽管有的蛇吃鸟蛋、青蛙，但是其他的一些蛇会吃破坏破坏庄稼的动物，对人类有帮助。并不是所有的蛇都有毒害，其他和主题不一致，而B（它能做一些对人类有益的事。）符合。
【小题3】细节理解题。根据Others eat pests（害虫）, mice and other animals that harm crops on farms.可知，蛇可以做有宝贵的工作，因为有的蛇吃害虫、破坏庄稼的老鼠和其他动物。所以选A。
【小题4】主题归纳题。文章介绍了优点蛇吃青蛙等，但是还有的蛇以破坏庄稼的害虫为食，对人类有贡献。所以选A。蛇有毒，所以不能把它当作好朋友来对待。只是对蛇看法转变而已。