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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 electricmotor-is

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

admin2009-03-13  45
问题     The idea of a fish being able to generate electricity strong enough to light lamp bulbs--or even to run a small electricmotor-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 centimetres 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.
选项 A、the capacity to generate electricity is the distinctive characteristic of the fish
B、the current travels in an upward direction from the positive side to negative side in torpedo’s electric cells
C、some fish can produce enough electricity to drive a number of electricmotors
D、the torpedo’s electric cells have a shape with six sides
答案D
解析 本题要求了解文章主旨的事实和细节。这一题要求我们在对全文整体理解后，并一一对照文中细节，才能做出选择。A认为“产生电的能力是鱼类的一种有别于其他生物的特性”。事实亡鱼类中只少数几种特殊的鱼有产生电的能力，并非所有的鱼类。因此A项是不正确的。B认为“电流经过电鳐细胞的正极向上到达负极。”而文中第二段很清楚写有电流从上方的正极向下流到下方的负极，B项是错的。 C认为“有些鱼能产生足以开动几台电动机的电量。”而文中对于鱼类所产生的电量的描述最惊人的也只能发动一台小电机。因此B项是不正确的。D项认为“电鳐的发电细胞的形状是六边形。”在文中第二段曾提到电鳐的发电细胞像蜂窝，由日常知识，我们知道蜂窝是六边形的，所以D是正确的。
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