检查沥青防腐层的电火花检漏谷仪，探头的输出电压一般要求在（）kV。
A.1~2
B.2~5
C.5~10
D.10~25
参考答案：C
I’m sorry, Bill. I _________ the book to you last week, but I was so busy that I forgot to do so.
A．must have returned
B．could return
C．should have returned
D．might return
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