单项选择题
When voltage and current developed in an AC circuit reach their peak values at the same time, the power factor is （）
A.lagging B.leading C.maximum D.minimum
单项选择题 While paralleling two AC generators using synchronizing lamps only, both lamps will go dark when the generators are （）.
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 （）.
