After taking part in several rounds of competition, the athlete         won first prize.

A．eventually

B．occasionally

C．frequently

D．usually

下列哪项效应是在用超声波治疗时不需要的效应（）

A.空化作用

B.声冲流作用

C.剪波效应

D.弥散效应

E.微细按摩效应