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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
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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。
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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