单项选择题
A.an electrical interlock system
B.an automatic paralleling trip switch
C.the synchronizing oscilloscope
D.the reverse current relay
单项选择题 A motor enclosure which protects against falling liquids is classified as （）
单项选择题 Universal motors will operate on AC or DC current, and are generally found in （）
单项选择题 An operational amplifier, as used in todays consoles, has a calculated gain of 5This means that when the input changes （）