________ the arrival of the police, I would have been robbed by two masked men.

A．Had it not been for

B．If it were not for

C．Had it been not for

D．If it would not be for

减压病是血液中哪种气体游离出造成的（）

A.氧气

B.氢气

C.氮气

D.氦气

E.氖气