单项选择题
Electric circuits are protected against overloads and short circuits by means of a/an （）.
A.circuit breaker B.amplifier C.diode D.capacitor
单项选择题 Ambient temperature is the （）.
单项选择题 You are attempting to parallel two AC generators and the synchroscope pointer is revolving in the slow directionThis indicates that the frequency of the incoming machine is （）.
单项选择题 The need for insulation cleaning may be determined by （）
