Two main techniques have been used for training elephants, which we may call respectively the tough and the gentle. The former method simply consists of setting an elephant to work and beating him until he does what is expected of him. Apart from any moral considerations this is a stupid method of training, for it produces a resentful animal who at later stage may well turn into a man-killer. The gentle method requires more patience in the early stages, but produces a cheerful, good-tempered elephant who will give many years of loyal service.
The first essential in elephant training is it assigns to the animal a single mahout who will be entirely responsible for the job. Elephants like to have one master just as dogs do; and are capable of a considerable degree of personal auction. There are even stories of half trained elephant calves who have refused to feed and pained to death when by some unavoidable circum stance they have been deprived of their own trainer. Such ext
A. early financial returns
B. their willingness to obey their trainers
C. the avoidance of anxiety in the elephant
D. that elephants are difficult to keep
Passage Two
Among the question of design, construction, and operation remaining to be solved before commercial airliners travel faster than sound is the difficult problem of sonic boom (声震) , the explosive sound generated when an object moves through the air at supersonic speed(超音速).
A sound is a pressure disturbance: a sonic boom, like other explosive sounds, is the result of an abrupt change in pressure. An airplane in subsonic flight produces weak changed in pressure, but because these disturbances travel at the speed of sound, they move faster than the airplane and stay in front of it. In effect, these disturbances warn the air to get out of the way, and the an does just jet, however, gets ahead of its own pressure disturbances. Consequently a wave of suddenly com pressed air--a shock wave--builds up and is thrown off like the wave ;hat spreads from the bow of a speedboat.
Can sonic booms be eliminated The answer is a categorical negative--they
A. explosive
B. caused by compressed tar
C. a pressure disturbance
D. shock wave
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