表面电极所记录的肌电图是（）

A.单个运动单位的电变化

B.多个运动单位电变化的综合

C.单个或多个运动单位肌纤维收缩的张力变化

D.肌肉兴奋时产生的动作电位变化

E.以上都是

Computers are already widely used in industry and in universities and the time may come when it ______ possible for ordinary people to use them as well.

A．is

B．will be

C．must be

D．may be