nough to light lampBulbs—oreven to mn a small electric motoris almost unbelievable，but several kinds of fish are able todo this．Even more strangely。this curious power hasBeen acquired inDifferent waysBy fishBe。longing to veryDifferent families． Perhaps theBest known are the electric rays，or torpedoes(电鱼)，of which several kindslive in warm seas,They posses on each side of the head，behind the eyes，a large organ consis—ting of a number of hexagonal shaped cells rather like a honeycomb．The cells are filled with ajeUy—like substance，and contain a series of flat electric plates．One side，the negative side，ofeach plate．is supplied with very fine nerves，connected with a main nerve coming from a specialpart of theBrain．Current passes from the upper，positive side of the organDownwards to thenegative，lower side．Generally it is necessary to touch the fish in two places，completing the cir-cuit，in order to receive a shock． The strength of this shockDepends on the size of the fish，but newlyBorn ones only about5 centimeters across canBe made to light theBulb of a pocket flashlight for a few moments， while a fully grown torpedo gives a shock capable of knocking a manDown，and，if suitablewires are connected，will operate a small electric motor for several minutes． Another famous example is the electriceel．This fish gives an even more poweIful shock．The system i8Different from that of the torped。in that the electric plates run longitudinally(纵向)and ale supplied with nerves from the spinal(脊骨)cord．Consequefitly，the current passesalong the fish from head to tail．The electric or gans of these fish are really altered muscles andlike all muscles are apt(1ikely)to tire，so they are not able to produce electricity for very long．The power of producing electricity may serve these flshBom forDefence and attack． （）It canBe seen from the passage that__________．
A.the torpedo’s electric ceils have a shape with six sides
B.some fish can produce enough electricity toDrive a number of electric motors
C.the current travels in an upwardDirection from the positive side to negative sidein torpedo’s electric cells
D.the capacity to generate electricity is theDistinctive acteristic of the fish
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