They _______ finding a solution to prevent the river being polluted.
A. set up B. set about
C. set out D. set off
They _______ finding a solution to prevent the river being polluted.
A. set up B. set about
C. set out D. set off
【解析】选B。句意: 他们着手寻找使河流不受污染的办法。set about 开始,着手,后接动名词;set out开始(做),后接不定式;set up设立,建立;set off出发,动身,使爆炸。