单项选择题
The most common source of excitation for synchronous motors is a/an （）.
A.low voltage battery B.motor attenuator set C.DC exciter generator D.AC supply
单项选择题 Before reassembling any machinery, you should （）.
单项选择题 Ammeters and voltmeters used in sinusoidal AC power systems indicate which of the following values of the waveforms measured?（）
单项选择题 Fuses placed in series with a thermal trip-type circuit breaker are used for （）.
