单项选择题

If a DC motor runs hot, the cause may be （）

A.high mica condition
B.low ambient temperature
C.clogged ventilation ducts
D.an open in the shunt field

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单项选择题
The unit of electrical resistance is the （）

A.ampere
B.volt
C.watt
D.ohm
单项选择题
Some large A-Cmotors are equipped with heatersThese could be （） (1)resistance heaters bolted directly to the frame (2)low voltage windings embedded in the motor windings

A.(1) only
B.(2) only
C.either (1) or (2)
D.neither (1) or (2)
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