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單項(xiàng)選擇題

Sparking at the brushes of a running motor could be an indication of （）.

A.normal operation
B.a dirty commutator
C.increased brush capacity
D.water vapor absorption

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單項(xiàng)選擇題

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

單項(xiàng)選擇題

The unit of electrical resistance is the （）

A.ampere
B.volt
C.watt
D.ohm

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