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问题 选择题

如图是一种新型锁--声纹锁。只要主人说出事先设定的暗语就能把锁打开，别人即使说出暗语也打不开。这种声纹锁辨别声音的主要依据是：

[ ]

A．音调

B．响度

C．音色

D．声速

答案

答案：C

选择题
若|a|=
1
2
，则a为（　　）
A．
1
2
B．-
1
2
C．±
1
2
D．±2
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选择题

Only in that way _____ find out how this kind of animal lived and then finished the research on time.[ ]

A. could they

B. they could

C. did they

D. they were able to

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