单项选择题
A.(1) only
B.(2) only
C.both (1) and (2)
D.neither (1) or (2)
单项选择题 The unit of electrical power is the （）
单项选择题 In an alternating current electrical system, a low system power factor is a direct sign of （）
单项选择题 An alternator is being paralleled with one on the lineAt the INSTANT the circuit breaker is closed, the frequency of the incoming alternator will normally （）.