定語從句中引導詞的選用主要看先行詞在定語從句中作什么成分或者是定語從句中缺什么成分。

　　1．定語從句中缺主語，修飾人時用who /that，修飾物時用which /that引導。如：

　　Is this the factory which /that makes TV sets？

　　The man who /that visited our school is from Australia．

　　2．從句中缺賓語，修飾人時用 who /whom /that或省略引導詞；修飾物時用which /that或省略引導詞。如：

　　Gone are the days which /that we spent together in the village．

　　He is the man who /whom /that I think to be worthy of our praise．

　　3．從句中缺時間狀語，用when或介詞+which引導。如：

　　The day finally came when /on which I was given a job．

　　We'll put off the outing until next week，when we won't be so busy．

　　4．從句中缺地點狀語，用where或介詞+which引導。如：

　　Please put the letter on the desk where /on which he can easily find it．

　　5．從句中缺原因狀語或先行詞是 reason時，引導詞用why /for which / that。如：

　　This is the reason why /for which / that he didn't come to the meeting．

　　6．從句中缺定語，人和物都用 whose引導。如：

　　A child whose parents are dead is called an orphan．

　　Please pass me the dictionary whose cover is black．

　　7．當先行詞是way時，其定語從句的引導詞用in which /that。如：

　　The way in which /that he looks at problems is wrong．

　　as

　　引導詞as可引導限制性定語從句，也可引導非限制性定語從句。

　　1．在固定詞組the same．．．a(chǎn)s，such．．．a(chǎn)s中，as引導限制性定語從句。如：

　　He is not such a fool as he looks．

　　I've bought the same dress as she is wearing．

　　2．當先行詞是整個主句時，可用 as /which引導非限制性定語從句。引導詞as和which的區(qū)別在于：

　�、賏s引導的非限制性定語從句可放于主句前、主句中、主句后，而which引導的非限制性定語從句一般放于主句后或句中。

　　②as常與從句中的know，see， hear，expect等動詞連用，也常用于as often happens，as is often the case（常有的事）等句子中；而which一般不用于以上情況。

　　③as有“正如”的含義，which沒有此含義。如：

　　As is well known，Shanghai is a big city．

　　Some of the roads were flooded， which made our journey more difficult．