定语从句是在复合句中修饰某一名词或代词的从句.被修饰的名词或代词叫做选行词,

　　而引导定语从句的词叫引导词,有关系代词和关系副词两类.

　　1．关系代词有：that,which,who,whom,whose,在定语从句中作主语、宾语中表语,whose

　　作定语.代人的有：who,whom,whose,that；代物的有：that,which,whose.例如：

　　ThemanwhohelpedyouisMrWhite.(who代人,在定语从句中作主语)

　　Thatistheperson(whom/who/that)youwanttosee.(whom,who,that代人,在定

　　语从句中作宾语,可省略)

　　I?mnotthefool(that)youthoughtmetobe.(that代人,在定从中作表语)

　　Adictionaryisausefulbookwhich(＝that)tellsusthemeaningofwords(which

　　或that代物,在定从中作主语)

　　2．关系副词有：when(指时间),where(指地点),why(指原因),在定语从句中作状语.

　　例如：Wouldyousuggestatime(when)wecanhaveatalk?(when可省略)

　　Thehousewheretheyliveisnotverylarge./Thisisthereasonwhyhedidnotcametothemeeting.

　　注意：不是表时间的先行词都用when引导定从,不是表地点的先行词都用where引导定从.