[originaltext] The idea of fighting a noise by making more noise sounds stra

游客2024-05-13  14

问题  
The idea of fighting a noise by making more noise sounds strange, but that’s exactly what motor engineers are doing in Germany and some other countries.
    Carmakers’ research and development laboratories have already proved that mixing in more noise with the help of loudspeakers can reduce the unwanted noise.
    Physicists have known about the technique for a long time. Sound is made up of pressure waves in the air. If two sound waves of the same frequency mix so that the highest point of one wave happens at the same time with the lowest point of the other wave, the result is no sound. Therefore, by producing a perfect copy of the noise and delaying it by half a wave cycle, we can kill the unwanted noise. Using this technique many carmakers are racing to develop noise-killing systems both inside and outside the cars.
    Another good thing about the use of noise-killing systems is that it saves the need for a silencer, which not only reduces the weight of a car, but also makes the motor burn less oil and work better.
    Some engineers believe that the noise-killing system will be used in most cars by 1996. But the carmakers haven’t decided if they will put it into production because it would add several hundred dollars to the cost of their cars.
Questions 29 to 31 are based on the passage you have just heard.
29. Which gives a general idea of how the noise-killing system works?
30. What can the noise-killing system do besides its main function?
31. Why isn’t the noise-killing system yet popular?

选项 A、It is still being tried out.
B、People still have their doubts.
C、It increases the cost of car production.
D、Carmakers are not sure if it is necessary.

答案 C

解析 选项中的It,being tried out,doubts,not sure等表明,本题可能考查It不被看好的原因。短文最后提到,一些工程师相信噪音消除系统在1996年将能应用到大多数汽车上,但汽车制造商还不确定是否批量生产,因为这种噪音消除系统会add several hundred dollars to the cost of…cars,即会提高汽车成本,故答案为C)。
转载请注明原文地址:https://tihaiku.com/zcyy/3596456.html
最新回复(0)