随着收费公路政策的实施、公路基础设施的改善以及汽车工业的发展，（）已成为人们选择出行的主要方式。

A.公路运输

B.铁路运输

C..水路运输

D.航空运输

—How I wish I had studied harder when I was in senior school! —If you had，you ________ a university student now.

A．are

B．would be

C．should

D．were