单项选择题
Tools with （）handles should be used to check electric circuit.
A.plastic B.metal C.stainless steel D.copper
单项选择题 Before doing maintenance on electrical equipment, you should （）.
单项选择题 While the parallel operation, （） must be used.
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.
