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  3. The idea of a fish being able to generate electricity strong enough to light lamp bulbs—or even to run a small electric motor—is

The idea of a fish being able to generate electricity strong enough to light lamp bulbs—or even to run a small electric motor—is

admin2012-07-17  62
问题     The idea of a fish being able to generate electricity strong enough to light lamp bulbs—or even to run a small electric motor—is almost unbelievable, but several kinds of fish are able to do this. Even more strangely, this curious power has been acquired in different ways by fish belonging to very different families.
    Perhaps the best known are the electric rays (鳐鱼)，or torpedoes (水雷鱼)，of which several kinds live in warm seas. They possess on each side of the head, behind the eyes, a large organ consisting of a number of cells which contain a series of flat electric plates. One side, the negative side, of each plate, is supplied with very fine nerves, connected with a main nerve coming from a special part of the brain. Current passes from the upper, positive side of the organ downwards to the negative, lower side. Generally it is necessary to touch the fish in two places, completing the circuit, in order to receive a shock.
    Another famous example is the electric eel (鳗鱼).This fish gives an even more powerful shock. The system is different from that of the torpedo in that the electric plates run along the length of its body and are supplied with nerves from the spinal cord (脊髓). Consequently, the current passes along the fish from head to tail. The electric organs of these fish are really altered muscles and like all muscles, they tend to tire easily, so they are not able to produce electricity for very long.
    The power of producing electricity may serve these fish both for defense and attack. If a large enemy attacks, the shock will drive it away; but it appears that the electric eel uses its current most often against smaller fish.
The purpose of the shock produced by electric fish is to______.
选项 A、protect themselves from being attacked
B、light up nearby waters
C、attack other fish or marine animals
D、both A and C
答案D
解析 本题问能放电的鱼放电的目的是什么。根据文章的最后一段内容，这一放电的功能使它们具有攻击和自卫能力。如果遇到庞大的敌人的攻击，放电电流会把敌人赶跑。但是，似乎电鳗在更多的情况下是用其电流攻击较小的鱼类。由此，我们可以推断出本题的正确答案应是D“保护自己不受攻击和攻击其他鱼类和海洋生物”。
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