单项选择题
A.5 volts, the output changes 10 volts
B.10 volts, the output changes 5 volts
C.2 volts, the output changes 10 volts
D.10 volts, the output changes 2 volts
单项选择题 Electrical failures in motors are caused by the breakdown of insulation, which may be caused by （）
单项选择题 A three-phase alternator operates at 450 volts with a power factor of 0~8.If the ammeter indicates 250 amperes, what should be the KW meter reading （）.
单项选择题 Sparking at the brushes of a running motor could be an indication of （）.