单项选择题
A.thousandth (10 to the-3rd power)
B.millionth (10 to the-6th power)
C.billionth (10 to the-9th power)
D.trillionth (10 to the-12th power)
单项选择题 A signal derived from a controlled function and returned to the initiating point is called a/an （）.
单项选择题 The purpose of a main switchboard circuit breakers reverse-power trip is to （）.
单项选择题 When you are making a high potential test on a piece of repaired electrical machinery, a rise in leakage current indicates （）.