定语从句 一、关系代词的用法 1．that和which的用法 (1)限制性定语从句中，必须用关系代词that的情况： ①当先行词是不定代词all，much，little，something，everything，anything，nothing，none，the one时。 You should hand in all that you have. ②当先行词前面被the only，the very，any，few，little，no，all等词修饰时。 This is the only thing that has been tried. ③当先行词是形容词最高级或先行词的前面有形容词最高级修饰时。 This is the best that has been used against pollution. ④当先行词是序数词或它前面有序数词修饰时。 This train is the last that will go to Suzhou. ⑤当先行词既有人又有物时。 Do you know the things and persons that they are talking about? ⑥当主句的主语是疑问词who或which时。 Which is the bike that you lost? ⑦有两个定语从句时，其中一个关系代词已用which，另外一个宜用that。 They secretly built up a small factory，which produced things that could cause pollution. ⑧当先行词在主句中作表语，而关系代词也在从句中作表语时。 Shanghai is no longer the city that it used to be.
(2)定语从句中必须用which的情况： ①在非限制性定语从句中，只用which，不用that。 Helen was much kinder to her youngest son than to the others，which，of course，made the others envy him. ②当动词短语中的介词提前时，只用which，不用that。 This is a house in which Lu Xun once lived.
注意：在一些固定搭配的动词短语中，由于动词和介词不可分割，因此不能把介词置于关系代词之前。 This is the pen (which/that) I'm looking for. 不可以说：This is the pen for which I'm looking. 2．who，whom和whose的用法 当先行词指人，在定语从句中作主语时，用who，不可省略；在定语从句中作宾语时，用whom/that，可以省略；在定语从句中作定语时，用whose，不可省略。 She is the girl who lives next door. That's the girl (whom/that) I teach. 3．“介词＋关系代词”引导的定语从句 “介词＋关系代词”引导定语从句时，关系代词只能用which(指物)或whom(指人)，即：介词＋which/whom。 (1)当介词放在关系代词的前面时，关系代词只能用which或whom，且不能省略。 They may start as a group of highschool students，for whom practising their music in someone's house is the first step to fame.
(2)在限制性定语从句中，当介词位于定语从句的末尾时，可用that/which(指物)，that/whom/who(指人)作介词的宾语，而且作介词宾语的关系代词可以省略。 This is the hero(that/who/whom) we are proud of.
(3)“复合介词短语＋关系代词which”引导的定语从句，这种结构引导的定语从句常与先行词用逗号分开，定语从句常用倒装语序。 He lived in a big house，in front of which stood a big tall apple tree.
(4)介词＋which/whom＋不定式结构。 The poor man has no house in which to live. ＝The poor man has no house to live in. ＝The poor man has no house in which he can live.
4．as和which的区别 (1)as引导的非限制性定语从句，既可在主句前，又可在主句后，有时还可插入主句中；而which引导的非限制性定语从句只能置于主句之后。相同的是两者都可替代主句的整个内容，而不是主句中的某一个词。
As is known to all，fish can't live without water. Smoking is harmful to our health，as we know. The weather turned out to be very good，which was more than we could expect. (2)当非限制性定语从句放在主句前面时，只能用as。 As is known to everybody，the moon travels round the earth once every month. ＝The moon travels round the earth once every month，as/which is known to everybody. ＝It is known to everybody that the moon travels round the earth once every month. ＝What is known to everybody is that the moon travels round the earth once every month.(后两句属名词性从句范畴) 另外，as多用于下列习惯用语中： as anybody can see正如人人都能看到的那样 as we had expected正如我们所预料的那样 as often happens正如经常发生的那样 as has been said before如上所述 as is mentioned above正如上面提到的 (3)当定语从句放在主句后面时，也并不是as就永远等于which。 ①当定语从句是否定句或表示否定时，只能用which。 He came here very late，which was unexpected(not expected)． Mr.Smith usually praises his student Rose in public，which she doesn't like at all. ②当as在从句中作主语时，后面常接动词的被动语态。如：be known，be said等。如果从句中行为动词是主动语态，一般用which作主语。 ③as常用在as often happens，as was said earlier，as I understand，as appears等结构中。 Jack has won the first prize，as often happens. ④as仍然保持作连词时常有的某种含义。 David is tall，as are my brothers. ⑤当非限制性定语从句的谓语后跟一个复合结构时，只能用which引导定语从句。 Betty always tells a lie，which her parents feel strange. 二、关系副词的用法 1．当先行词在定语从句中作状语时，要用关系副词。 I still remember the day when I first came to Beijing.(when＝on which) Can you tell me the office where he works？(where＝in which)
2．介词＋关系代词(which)＝where/when。有时为表达清楚，还可以在关系副词where/when前加介词from，to等。 China is the birthplace of kites，from where kites spread to Japan and Korea.