everybodymustdoeverythinghecan——wastewaterfromrunningintorivers.
A.keepB.keptC.tokeepD.keeping(为什么)
2.It____behim.
为什么是can't不是mustn't
3.sincejune1stlastyear,allthesupermarketshave___freeplasticbags.
为什么是stoppedproviding而不是tostopproviding