单项选择题
Voltage will always lead current in a/an （）
A.capacitive circuit B.inductive circuit C.magnetic circuit D.resistive circuit
单项选择题 The number of cycles per second occurring in AC voltage is known as the （）
单项选择题 Complete maintenance of electrical motors should include periodic checks for machine （）
单项选择题 The frequency of an alternator is controlled from the main switchboard by adjusting the（）
