题型:阅读理解 题类:常考题 难易度:普通
重庆市第一中学2018届高三上学期英语11月月考试卷
Blind people usually possess one advantage over other people who can see. Their sense of hearing is far more acute. Bats, whose sight is poor, use a sound location system to help them avoid blocks in the dark. They send out pulses of sound waves, pitched at 50,000 cycles per second, far above the limits of the human ear, which can hear sounds up to frequencies of about 20,000 cycles per second. As the echoes bounce back off obstacles such as trees and walls, the bats are able to take proper action.
The first steps to help blind people to see with sound are based on exactly the same principle. The sound is given off by an ultrasonic (超声的) torch, whose shape is different from a normal electric torch. It is double-barreled. It works in a similar way to a sonar (声呐) unit on a warship or submarine. The unit's transmitter sends out pulses of ultrasonic waves at the same frequency as the bat and the receiver picks up the returning echoes. Because these are still above the frequency at which the human ear can pick them up. The echoes are filtered (过滤) through circuits that turn them into “bleeps” which can be clearly heard before passing them into headphones.
This means that a person holding the torch can point it ahead of him and scan the area for obstacles over a range of about 25 feet. If there are no return echoes coming through the headphones, then there is nothing in the way. If echoes do come back, then the closer the obstruction the faster the succession of bleeps and the deeper the pitch of each bleep. With practice, the torch could help a blind person to lead a more normal life.
At present, the experimental ultrasonic torch requires a shoulder bag to carry the batteries, cables for the power supplies and earphones, as well as the torch itself. Fortunately, reducing the size of the electronic equipment is progressing and it should not be long before the whole set-up can be reproduced in a form small enough to fit into a pair of glasses. The wearer would face in the direction he wanted to check, and lift or lower his head just as a sighted person would.
a. Helping the blind to walk.
b. Helping deaf children to watch sports.
c. Helping the blind to lead a better life.
d. Being used in a warship or submarine during a war.
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