We must try our best ________ pollution ________ again and again.A.to stop; happenB.to stop; from happeningC.stopping; happeningD.stopping; to happen
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B解析此题考查的是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., e to do sth.等，另外，此题还考查了另一个重要句型stop...from doing sth.。