单项选择题
A.residual magnetism
B.voltage regulator
C.electrical current for excitation
D.the other running generator
单项选择题 “380V/220V Y/△” noted on the nameplate of a non-synchronous motor means that（）
单项选择题 The nameplate of an AC non-synchronous motor shows that running speed is 1460r/minfrequency 50HzYou can infer that the number of magnetic poles is（）
单项选择题 With one or more cylinders out of operation, the engine speed must be reduced because（）