单项选择题
The need for insulation cleaning may be determined by （）
A.visual inspection for dirt accumulation B.high megger readings C.low operating temperature D.the time period since the last cleaning
单项选择题 Voltage will always lead current in a/an （）
单项选择题 The number of cycles per second occurring in AC voltage is known as the （）
单项选择题 Complete maintenance of electrical motors should include periodic checks for machine （）
