问题补充：
To prevent the air ,something will have to .
A. to pollute…take
B. from being polluted ..be done
C. to be polluted…be taken
D. from polluted… be done
答案：
A. to pollute…take
(答案→)B. from being polluted ..be done
C. to be polluted…be taken
D. from polluted… be done
解析：prevent..from doing 是固定搭配，意思是：阻止..做….
