A young man         glasses came        the office . He had an old bag          his arm .

A．without ; in ; in

B．with ; into ; under

C．in ; out of ; under

D．with ; in ; on

调频泵切换到工频泵操作中，启动工频泵前应（）。

A.开排污阀

B.开进口阀

C.开出口阀

D.关出口阀