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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--

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

admin2013-03-11  58
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, or torpedoes(电鳐), 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 hexagonal shaped cells rather like a honeycomb. The cells are filled with a jelly-like substance, and 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.
     The strength of this shock depends on the size of the fish, but newly born ones only about 5 centime-tres across can be made to light the bulb of a pocket flashlight for a few moments, while a fully grown torpedo  gives a shock capable of knocking a man down, and, if suitable wires are connected, will operate a small electric motor for several minutes.
    Another famous example is the electric eel. This fish gives an even more powerful shock. The system is different from that of the torpedo in that the electric plates run longitudinally(纵向) and are supplied with nerves from the spinal(脊骨) cord. 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 are apt (likely) to tire, so they are not able to produce electricity for very long.
    The power of producing electricity may serve these fish both for defence and attack.
The reason why the electric eel is able to give more powerful shock is that______.
选项 A、the working system of the electric plates in the eel is the most effective
B、the working system of the electric plates in the eel is far inferior to those in the torpedo
C、compared with those in the torpedo, the working system of electric plates in the eel is more direct and efficient
D、compared with other electric fish, the eel possesses much more electric plates
答案C
解析 在第四段中，作者详细地说明了电鳗的发电系统，电鳗的发电组织是纵向的，由脊骨的神经供电，因而电流从头至尾流动。而电鳐的发电器官是蜂窝状且分布于头部两侧，可以看山电鳗由于其脊骨神经供电，电流可直接由头传至尾，较顺畅，可推断出电鳗的发电系统较之电鳐更直接也更有效一些，所以应选C项。
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