单项选择题
If a voltmeter is connected across a line, it must be protected with a（）
A.shunt B.high-resistance coil in the armature circuit C.low-resistance coil in the armature circuit D.shunt and a coil of high resistance
单项选择题 When current and voltage reach maximum values at the same time, the power factor is（）
单项选择题 Which is an acceptable means of correcting high mica between commutator bars?（）
单项选择题 Generator brushes are staggered to（）
