单项选择题
Which of the following devices are protected from being motorized by a reverse-power relay?（）
A.Alternators B.Wave guides C.Exciters D.Amplidynes
单项选择题 If the length of a wire is halved and the cross-sectional area is doubled, the resistance will be （）
单项选择题 AC and DC generators are similar in that they （）
单项选择题 To increase the frequency of an operating AC generator, you should （）
