单项选择题
Tools with （）handles should be used to check electric circuit.
A.plastic
B.metal
C.stainless steel
D.copper
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单项选择题
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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While the parallel operation, （） must be used.
A.ammeter
B.voltmeter
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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
