Question

We must try our best ________ pollution ________ again and again.

1. A.
   to stop; happen
2. B.
   to stop; from happening
3. C.
   stopping; happening
4. D.
   stopping; to happen

Answer 1

B
此题考查的是try one's best to do sth.，此处动词不定式做状语，表示目的，类似的词组有stop to do sth., go to do sth., come to do sth.等，另外，此题还考查了另一个重要句型stop...from doing sth.。