Our bad living habits will destroy the earth. Only by changing      we live 

       save the earth.

A．what; can we

B．how; can we

C．where; we can

D．how, we can

提高医疗质量的物质基础是（）

A.治疗技术

B.医疗设备

C.规章制度

D.医德医风

E.经济效益