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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  47
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.
Usually you will not get a shock until you touch______.
选项 A、a torpedo in one place
B、the water nearby it
C、its main nerve connected with fine nerves
D、a torpedo in two places
答案D
解析 本题是一道根据文章所提示的具体细节进行推断的题目。问通常你只有在什么情况下才会受到电鳐鱼的电击。根据文章第二段关于电鳐鱼放电的原理部分，在电鳐鱼的头上每一侧眼睛的后面均有一个很大的、由几个小腔组成的器官，内含一组电极片。各电极片的一面，即负极面，具有十分敏感的神经，这些神经与通往大脑一个特殊部分的主神经相连。电流通过器官上面，即正极面向器官下面的负极面流动。一般说来，需要触摸到鱼身体的两个部位才能形成电流回路，受到电击。因此，本题的正确答案应是D“只有摸到电鳐鱼身体的两个部位才会受到电击”。
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