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單項選擇題

Before doing maintenance on electrical equipment, you should （）.

A.turn off power first
B.turn on power first
C.with a test pen in hand
D.tell C/E

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單項選擇題

While the parallel operation, （） must be used.

A.ammeter
B.voltmeter
C.synchroscope
D.A+B+C

單項選擇題

When the bearing becomes dry from lack of oil, the motor shaft may heat to （）an extent （） it welds itself to the bearing.

A.either；or
B.neither；nor
C.such；that
D.so；that