Great efforts to increase wheat production must be made if bread shortages ___avoided.

问题描述:

Great efforts to increase wheat production must be made if bread shortages ___avoided.
A.will be
B.are to be
C.can be
D.were to be
选B,D哪错了?

B表示将来时态
如果想要阻止粮食短缺的话就要加大粮食生产的力度
D表示过去时态