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（）
A.2 B.4 C.6 D.8
单项选择题 With one or more cylinders out of operation, the engine speed must be reduced because（）
单项选择题 A few spots of turbocharger can be caused by（） ①crash stop of engine ② rapid increased of engine speed
单项选择题 The function of synchronous compensating machine is to（）
