压气系统包括自动注油器、冲击操纵器、（）等组成。
A.压力表
B.推压操纵器
C.送杆操纵器
D.风管
参考答案：B, C, D
Mr Smith ____ a book about China last year but I don't know whether he has finished it. [ ]
A. has written
B. wrote
C. had written
D. was writing
