填空题
Instructions: There is one passage in this
section with 5 questions. Read the passage quickly and answer the questions on
the Answer Sheet. 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, 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 fiat 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 and are supplied with nerves from the spinal 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 to tire, so
they are not able to produce electricity for very long.
The electric catfish of
the Nile and of other African fresh waters has a different system again, by
which current passes over the whole body from the tail to the head. The shock
given by this arrangement is not so strong as the other two, but is none the
less unpleasant. The electric catfish is a slow, lazy fish, fond of gloomy
places and grows to about 1 metre long; it is eaten by the Arabs in some
areas.
The power of producing electricity may serve these fish
both for defence and attack. If a large enemy attacks, the shock will drive it
away; but it appears that the catfish and the electric eel use their current
most often against smaller fish, stunning them so that they can easily be
overpowered.
For answers 51-55, mark
Y(for YES) if the statement agrees with the information given in
the passage;
N (for NO) if the statement contradicts the
information, given in the passage;
NG(for NOT GIVEN) if
the information is not given in the passage.