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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单项选择题

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

A.ampere
B.kilovolt
C.watt
D.farad

单项选择题

A.wasted energy
B.efficient operation
C.a short in the exciter field windings
D.an excessive number of minor system grounds