Why would an animal kill itself? It seems a strange question, and yet it is one that has m

Why would an animal kill itself? It seems a strange question, and yet it is one that has made some scientists curious for a long time. For there is a kind of animal called lemming（旅鼠）, that periodically killed themselves together, and no one knows just why!
The small creatures which live in the Scandinavian mountains, feed on a diet of roots and special insects and live in nests they dig underground. When their food supply is large, the lemmings live a normal and undisturbed life.
However, when the lemmings’ food supply becomes too low to support the population, a singular migration（迁徙）begins. The lemmings leave their nests in groups. Great numbers of them begin to travel across the Scandinavian plains, a journey that may last weeks. The lemmings eat everything in their path, continuing their long march until they reach the sea.
The reason for what follows remains unbelievable to naturalists. Upon reaching the coast, the lemmings do not stop but swim by the thousands into the sea. Most stay afloat only a short time before they tire, sink and drown.
A common theory for this mass self-killing is that the lemmings do not realize that the ocean is such a huge body of water in their cross-country journey, the animals must cross many smaller bodies of water, such as rivers and small lakes. They may think that the sea is just another such swimmable path to go through. But no final answer has been found to the strange happening.
【小题1】The passage is mainly about . A．how lemmings find foodB．why animals kill themselves C．the lemmings’ self-killingD．the food supply in the Scandinavian mountains【小题2】A reason for the lemmings’ self-killing might be that they . A．go mad from a lack of foodB．hope to find fish for foodC．decide to reduce the populationD．think they can cross the sea【小题3】Why are scientists curious about the lemmings’ behavior? A．Because they are the only animals that live in Scandinavia. B．Because it is very unusual for animals to kill themselves. C．Because of the amount of food they can eat on their march to the sea. D．Because they can gather together in such huge numbers.【小题4】The underlined word “singular” means . A．unusualB．singleC．wonderful D．commonC

(答案→)C 解析：文章大意：介绍奇异的旅鼠集体自杀现象及对其原因的推测。【小题1】C 主旨大意题第一段引出旅鼠定期集体自杀的话题，然后介绍他们的习性，接下来因为食物供应不足而进行迁徙，到达海边，然后集体渡海，体力不支死亡。最后一段是人们对于这种现象的推测。文章主要介绍的是旅鼠的自杀现象。【小题2】D 细节理解题根据最后一段：旅鼠可能没有意识到海洋那么广阔，他们可能认为大海不过是可以游过去的。【小题3】B 推理判断题根据文章最后一句：But no final answer has been found to the strange happening. 但是对于这种奇特现象至今还没有最终的解答，导致科学家们对于旅鼠的异常行为非常好奇。【小题4】A 词义猜测题旅鼠的这次迁徙导致了不同于寻常动物迁徙的结果，所以这是unusual: 不同寻常的；非同寻常的。single: 单一的；单身的；单程的；wonderful: 奇妙的；极好的；common: 共同的；一般的；普通的。

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