第1个回答 2013-07-06
Something must be done to prevent the earth from being polluted.Something 主语 must be done谓语 含情态动词的被动语态 to prevent the earth from being polluted.动词不定式短语 做目的状语being polluted是动名词的被动形式 作介词宾语 与地球是被动关系这是 prevent sth from doing sth 句型 防止某物做某事