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  3. The Magic of Sound Music is one of the most beautiful forms of artistic expressions ever invented. In movies and plays, musi

The Magic of Sound Music is one of the most beautiful forms of artistic expressions ever invented. In movies and plays, musi

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问题                         The Magic of Sound
    Music is one of the most beautiful forms of artistic expressions ever invented. In movies and plays, music has an added function: it not only moves people but also can shock people.
    Our eardrums can withstand sound within 20 to 80 decibels(分贝). Once sound exceeds this limit, even beautiful music will become ear-splitting noise and harm health. A strong blast(响声)of high sound can twist and break a solid iron sheet. High sound of 150 decibels can kill a healthy rat.
    In movies, sometimes the hero can produce a sound that ordinary people can’ t hear and only those who have the same ability can feel. In nature, there is actually sound that is beyond our hearing. In physics, the sound that exceeds 20, 000Hz is called ultrasonic(超音波的). Dolphins, whales and bats can make such high-frequency sound. It does no harm to health.
    Sound less than 20Hz is called infrasonic(次声)waves. When we move, the air will vibrate. The vibration of air can produce infrasonic waves. As the frequency of infrasonic waves is close to that of people’ s internal organs, infrasonic wave may cause resonance(共振)in human bodies. As a result, people’ s vision may weaken and internal organs may rupture(断裂). However, whether an infrasonic wave can be used as a weapon depends on its intensity. If its intensity is very low, it won’ t damage internal organs or a person’ s health. If the intensity of infrasonic wave exceeds 160 decibels, it is extremely harmful. When wind blows at a force of 3 or 4 over the sea, it will produce infrasonic waves of several decibels. Only typhoons can produce infrasonic waves of over 100 decibels. At present, scientists can only produce infrasonic weapons in the lab with the help of advanced scientific tools and powerful electric power.
It can be found from the last paragraph that infrasonic waves______.
选项 A、are harmless to people’ s health
B、exist in people’ s internal organs
C、can be used as deadly weapons
D、can improve eyesight
答案B
解析 根据第四段第四句可知，当次声波的频率与人体内部器官的频率相当时，就会对人体造成危害，又由常理可知振动会产生声音，可推断出人体内存在次声波，因此选择B项。只有当次声波频率与人体内部器官的频率相近时，次声波才会对人有害，所以A项错误；只有超过160分贝的次声波才能被用作致命武器，并且由最后一段最后一句“At present，scientists canonly produce infrasonic weapons in the lab…”可知，次声波用作致命武器还只是实验室的实验结果，现实中并没有出现，所以C项错误；最后一段没有表明次声波可以改善视力，所以D项错误。
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