—Do you like that _______?

—Yes, I do. I often go to his concert. [ ]

A. pianist  

B. golfer  

C. dentist    

D. teacher

活塞式压缩机采用（）调节方法的优点是设备简单，操作方便，可作无级连接调节，缺点是不经济。

A.切断吸气

B.节流吸气

C.回流

D.全程顶开吸气阀