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问题
单项选择题
噪声评价数N等于哪个倍频带声压级( )
A．125Hz
B．250Hz
C．500Hz
D．1000Hz
答案
参考答案：D
选择题
He has learned ____, no matter what happens and how bad ____ seems today, life goes on and it will be better
tomorrow.
A. that; it
B. it; that
C. it; it
D. that; that
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问答题 简答题
先导化合物的来源有四种来源
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