单项选择题
A circuit that has one wire in contact with the hull of the ship is a（）
A.series circuit B.grounded circuit C.short circuit D.closed circuit
单项选择题 If two AC generators are to be operated in parallel, the load is distributed evenly by（）
单项选择题 If a voltmeter is connected across a line, it must be protected with a（）
单项选择题 When current and voltage reach maximum values at the same time, the power factor is（）
