当这个句子或短语做先行词时,必做成非限定性定语从句.关系代词可用which或as.注意:1.当在从句中做主语,若谓语动词是非be动词,必须使用which.其他情况,则可通用.2.当从句在主句前面时,则必用as. he said he was a king,which(as) was a lie.做主语,谓语为be. he said he was a king,which surprised me.做主语,谓语为非be. he said he was a king,which(as)i didn't believe.做宾语 As we all know,he is a cheat.从句在前