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 （）.
A.90~0 kw B.127~27 kw C.155~70 kw D.194~85 kw
单项选择题 Sparking at the brushes of a running motor could be an indication of （）.
单项选择题 If a DC motor runs hot, the cause may be （）
单项选择题 The unit of electrical resistance is the （）
