单项选择题
A.plastic B.metal C.stainless steel D.copper
Before doing maintenance on electrical equipment, you s...
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
While the parallel operation, （） must be used.A.ammeter...
单项选择题While the parallel operation, （） must be used.
A.ammeter B.voltmeter C.synchroscope D.A+B+C
When the bearing becomes dry from lack of oil, the moto...
单项选择题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
