下列电路元件符号表示电动机的是（ ）
A．
B．
C．
D．
A、灯泡；
B、电流表；
C、电动机；
D、电阻．
故选C．
--- Where is Jack?
--- He _________ football on the playground with those AFS students, but I am not sure.
A．must be playing
B．must have played
C．may be playing
D．may have played
简述联邦制的主要内容。
