门卫员在进行格斗姿势训练时，要求转身，撤步，拉拳屈膝要（）一致。
A.30
B.60
C.90
D.120
参考答案：B
You'd better walk _______ the footbridge. The shopping mall is on the other side of the street. [ ]
A. over
B. through
C. across
D. around
离心式压缩机若发生喘振如何消除？
