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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--

admin2011-06-28  66
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 be- longing to very different families.
    Perhaps the best known are the electric rays, or torpedoes (电鱼), of which several kinds live in warm seas. They posses 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 centimeters 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 arc 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 or gans 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.
Usually you will not get a shock by touching the electric ray in one place only because ______.
选项 A、the current in one place is not strong enough to give a shock
B、the fish’s electric cells are filled with jelly-like substance
C、to complete the circuit, you have to touch the fish in two places
D、a torpedo’s electric cells contain more than one electric plates
答案C
解析
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