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

A.time-delay protection
B.short-circuit protection
C.short duration surge protection
D.sustained overload protection

单项选择题

A.a magnetic operating coil
B.normally open line contacts
C.thermal-overload protection
D.a momentary-contact start button

单项选择题

A.60
B.120
C.180
D.360