单项选择题
A.running at the same speed
B.grounded
C.of the same polarity
D.in phase
单项选择题 Electric circuits are protected against overloads and short circuits by means of a/an （）.
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 （）.