which和as引导非限制性定语从句时的区别

whichas1、语义的区别当主句和从句语义一致时,用as；He made along speech,as we expected。当主句和从句语义转折不一致时,用which,He made along speech,which was unexpected。2、位置的区别看到句首一定用as,which 不可能放在句首。as we all know,as is mentioned aboveas often happensas is often the caseAs is well known3、含义的区别as有“正如”的含义,which没有此含义。As is well known,Shanghai is a big city． Some of the roads were flooded,which made our journey more difficult．4、否定句用which Tom drinks a lot everyday,which his wife doesn’t like at all。