动脉血PaCO₂的参考值范围是（）

A.45～55mmHg

B.30～40mmHg

C.45～50mmHg

D.35～45mmHg

E.35～40mmHg

— What  are you going to do this weekend?

— ______, I’m going to visit the Nature Museum.

A．If anything

B．If ever

C．If possible

D．If busy