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单选题
Sound is audible to human beings only if the frequency is______.
A

fewer than about 20 vibrations per second

B

more than about 20,000 vibrations per second

C

about in a range of 20 to 20,000 vibrations per second

D

120 vibrations per second


参考答案

参考解析
解析:
细节题。文章第二段倒数第二句提到“The human ear is usually not sensitive to frequencies of fewer than 20 vibrations per second, or more than about 20,000 vibrations per second”,即“人的耳朵对每秒震动20次以下或2万次以上的声音不敏感”,因此C项正确。
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