Mr. Zhang once taught in a remote village in Anhui province as a volunteer, _______was accessible only on foot.

A．where

B．which

C．that

D．what

—How did the global financial crisis ________？

—I’m not quite sure. Anyhow, it is a very important problem facing us.[ ]

A. come up        

B. come about      

C. come along        

D. come around