电流指单台或多台用电设备持续为（）左右的最大负荷电流。
A.1s
B.5s
C.15s
D.30s
参考答案：A
声波可以用来_________钟表等精密机械，外科医生利用_________除去人体内的结石。
Annie _______ to the party. She had a wonderful time with us.
A．invites
B．is invited
C．was invited
D．has invited
