如果某三相异步电动机的极数为4级，同步转速为1800转/分，那么三相电流的频率为: A.
50赫兹 B.
60赫兹 C.
45赫兹 D.
30赫兹

A．what exchange rate regime a country should employ
B．homework
C．which agency should be directing government policies
D．who oversees domestic vs. international policy objectives