------- Now you can see how serious the situation is !

-------- Yes.  We _____something before it got so bad .

A．should do

B．must do

C．must have done

D．ought to have done

哪种滑阀中位机能不能实现锁紧（）。

A.O型中位机能

B.H型中位机能

C.M型中位机能

D.P型中位机能