题目内容

当悬挂的吸声体面积与室内所需噪声治理面积之比为()左右时，其吸声效率最高

A. 10%
B. 25%
C. 50%
D. 70%

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链传动是借助链和链轮间的( )来传递动力和运动的

A. 摩擦
B. 粘接
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A. qualification
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C. certificate
D. proof

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A. deriving
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