单项选择题

Ammeters and voltmeters used in sinusoidal AC power systems indicate which of the following values of the waveforms measured?（）

A.Peak value
B.Root-mean-square value
C.Average value
D.Maximum value

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单项选择题
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A.time-delay protection
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单项选择题
The main difference between a motor control circuit containing low voltage protection and low voltage release is that the latter contains （）.

A.a magnetic operating coil
B.normally open line contacts
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