单项选择题
In order to change the direction of rotation of a D-Cmotor （）
(1) the field leads must be changed
(2) the input leads must be changed
A.（1）only
B.（2）only
C.either（1）or（2）
D.neither（1）or（2）
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If a small electric motor is immersed in salt water it should be （） (1) washed in fresh water (2) dried in an oven
A.(1) only
B.(2) only
C.both (1) and (2)
D.neither (1) or (2) -
单项选择题
The unit of electrical power is the （）
A.ampere
B.kilovolt
C.watt
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单项选择题
In an alternating current electrical system, a low system power factor is a direct sign of （）
A.wasted energy
B.efficient operation
C.a short in the exciter field windings
D.an excessive number of minor system grounds
