单项选择题
To increase the frequency of an operating AC generator, you should （）
A.increase the field excitation B.decrease the field excitation C.increase the number of magnetic poles D.increase the speed of the prime mover
单项选择题 When measuring AC current flow, you must always connect the meter （）
单项选择题 The frequency of an AC generator is adjusted by means of the （）
单项选择题 When the current flow through a copper wire increases, its （）
