If we the earth we must take action before it is too late. A. will save B. are to save C

问题补充：

If we the earth, we must take action before it is too late.

A. will save

B. are to save

C. are about to save

D. are saving

答案：

A. will save

(答案→)B. are to save

C. are about to save

D. are saving

解析：原句意思是，如果我们要拯救地球，那么在太迟之前我们必须采取行动。be to do结构，在条件状语从句中用一般现在时表示将来，答案为B。