我国电网以_______ 供电,频率为_______ Hz,即电流方向每秒钟改变_______次.
交流;50;100
What does you brother do?[ ]
A. He works very hard.
B. He is outgoing and friendly.
C. He is a sales assistant.
D. He is tall with curly hair.
德国早期养老保险基金实行的筹集模式是( )
A.现收现付式
B.完全积累式
C.部分积累式
D.预收预付式