单项选择题
The main purpose of an electric space heater installed in a large AC generator is to （）
A.prevent the windings from becoming brittle B.prevent moisture from condensing in the windings during shutdown C.prevent acidic pitting of the slip rings D.keep the lube oil warm for quick starting
单项选择题 A transformer in an electric circuit serves to （）
单项选择题 When placed in a magnetic field, which of the materials listed will maintain the highest permeability?（）
单项选择题 An ohmmeter can be used to measure（）
