三相异步电动，电源频率f=50HZ，转差率为0.5，磁极对数为4，则其转速为（）m/s。
A.375
B.400
C.470
D.500
参考答案：A
The boys green sports shirts are the fans of Guo'an Team. [ ]
A. with
B. in
C. at
D. from
