在Linux下，有一个命令叫做which，它可以在Path中寻找某个命令所在的目录并显示出来。 Linux下：
pron.哪一个； 哪一些； 哪个； 那，指前面提到的事物
adj.哪一个； 哪一些；
1、Soon after getting off his horse, the captain appeared at the second storey windows, fromwhere he could see nothing but trees.下马不久，上尉就出现在二楼的窗口了。他从那里除了树木什么也没看到。(引导定语从句)
划线部分相当于…, and from at the windows…不可变为from which…，直接用where不如用from where更具体。
2、She climbed up to the top of the hill,from where she could have a good view of the whole town.她登上山顶，从那里她可以一览全城风光。（引导定语从句）
划线部分相当于…, and from on the top of the hill或from on the top of which…,不可变为from which，也可直接用where引导，但语义较为含糊，不如用from where更加生动、形象、具体。
3、We went up to the roof ,from where we had a good view of the procession.我们爬到屋顶，在那儿我们可以一览整个行进队伍。（引导定语从句）
划线部分可理解为and from on the top of the roof或from on the top of which，用from which是不对的，直接用where仍显不具体，不形象。
4、China is the birth place of kites, from where kiteflying spread to Japan,Korea,Thailand and India.中国是风筝的故乡，在那里风筝传到日本、朝鲜、泰国和印度。
这里from正与下文的spread to构成一个整体，可理解为from near/around this place，如若把from where换为where显然是讲不通的，改成from which,能够讲得通，但不太符合英语习惯。
5、The car stopped suddenly only a few inches from where I stood.那辆小汽车就在我站的地方仅几英寸处突然停下了。（引导状语从句）这里的划线部分中where引导的是宾语从句，与from一起作地点状语从句。
例句1:look over there!some people are standing under the big tree,___ you can enjoy the whole view. A.which B.from which C whereD from where
分析：where代表under the tree这个地方，如果用which就只能代表the big tree,这句话的意思不是Enjoy the whole view from the big tree.而是from under the big tree.介词后接介词短语的例子还是常见的。实际上这个句子完整的应该是You can enjoy the whole view from the place under the big tree. the place被省略了。 该句属于定语从句。
例句2:He stood by the window, ______ he could see what was happening outside.
A. where B. which C. from which D. from where
两者都可指物，常可互换。其区别主要在于：
1. 引导非限制性定语从句时，通常要用which：
The current, which is very rapid, makes the river dangerous. 水流湍急，使这条河很危险。
He has to work on Sundays, which he doesn’t like. 他得在星期天工作，他是不喜欢这样的。
The London team, which played so well last season, has done badly this season. 伦敦队上一个季度打得很好，这个季度却打得很差。
2. 直接放在介词后作宾语时，通常要用which：
She may be late, in which case we ought to wait for her. 她可能晚到，那样我们就要等等她。
The documents for which they were searching have been recovered. 他们找寻的文件已找到了。
This morning some port wine came, for which I have to thank you. 今天早上送来一些波尔图葡萄酒，为此我得向你道谢。
注：有时“介词+which”引导的定语从句可以转换成“介词+which+不定式”结构：
He had only the long nights in which he could study. =He had only the long nights in which to study. 他只有漫漫长夜可用来学习。
He had a couple of revolvers with which he could defend himself.= He had a couple of revolvers with which to defend himself. 他只有一两把手用来自卫。
3. 当先行词是下列不定代词或被它们修饰时much, little, none, all, few, every(thing), any(thing), no(thing) 等时，通常用that：
All that she lacked was training. 她缺的只是训练。
Have you everything that you need? 你需要的东西都有了吗？
The sleeping man’s subconscious mind retained everything that was said around him. 这位酣睡的人头脑的下意识能记住他周围的人说的话。
She would never do anything that was not approved of by her parents. 她父母不赞同的事她绝不会做。
4. 当先行词有the very, the only, the same 等修饰时，通常用that：
This is the only example that I know. 我知道的例子只有这一个。
Those are the very words that he used. 那是他的原话。
5. 当先行词有形容词最高级或序数词(包括last, next等)等修饰时，通常用that：
This is the best dictionary that I’ve ever used. 这是我用过的最好的词典。
The first thing that you should do is to work out a plan. 你应该做的第一件事是订个计划。
6. 当关系代词在定语从句中用作表语时，通常用that：
China is not the country (that) it was. 中国已不数去的中国了。
7. 当先行词是一个既指人又指物的并列词组时，通常用that：
They talked about the persons and things that most impressed them. 他们谈论了使他们印象最深的人和事。
8. 当要避免重复时：
Which is the course that we are to take? 我们选哪门课程？
1、在后置的非限制性定语从句中代替上文出现的事物或情况(单数或复数)。
2、在问句中作为疑问代词，在名词从句中作为连接代词用，其含义为“哪个、哪些”。
3、如果非限制性定语从句的先行词不是指主句内容，而是指具体的人、时间、地点，则不用which。
which引导定语从句的时候，在从句中作主语，宾语或是表语，分享了定语从句which与where用法。
一、关系副词与“介词+which”互换的情形
当“介词+ which”在定语从句中作时间、地点和原因状语时，可以用相应的关系副词when, where和why来替换。
1. when根据情况可以等于in which, at which, on which等。如：
The day when (=on which) she arrived was Thursday. 她到的那天是星期四。
July and August are the months when (=in which) the weather is hot. 七八月是天气很热的月份。——摘自《英语常用词多用途词典》（金盾出版社）
这种替换有时出现在非限制性定语从句中。如：
We’ll put off the picomic until next week, when (=by then) the weather may be better. 我们将把野餐推迟到下星期，那时天气可能会好一点。——摘自《张道真英语语法》（商务印书馆）
2. where根据情况可以等于in which, at which, on which等。如：
This is the hotel where ( =in which / at which) they were staying. 这就是他们当时住的旅店。——摘自《英语常用词多用途词典》（金盾出版社）
Do you remember the place where (=at which) we had lunch? 你记得我们吃午饭的地方吗？ ——摘自《英语用法指南》（外研社）
这种替换有时出现在非限制性定语从句中。如：
The Tower of London, where (=in which so many people lost their lives, is now a tourist attraction. 在伦敦塔中曾有许多人丧命，它现在是旅游胜地。——摘自《朗文英语语法》（外研社）
3. 关系副词若要换成“介词+which”只能是for which。如：
The reason why (=for which) I came here was to be with my family. 我到这里来的原因是要跟我的家里人在一起。——摘自《英语用法指南》（外研社）
My success in business, the reason why (=for which) he dislikes me, has been due to hard work. 他为我在事业上的成功而不喜欢我，我的成功归功于我努力工作。——摘自《朗文英语语法》（外研社）
但是，反过来，for which并不一定能换成why。如：
The documents for which they were searching have been recovered. 他们找寻的文件已经找到了。（此句中的for which也不能换成why，理由同上句）——摘自《高中英语语法详解》（湖南大学出版社）
二、关系副词与“介词+which”不能互换的情形
1. 有些语境需要用特定的介词来明确其关系，此时若换成关系副词，则会导致意思不明确或句意不能通顺。如：
The ladder on which I was standing began to slip. 我脚下的梯子开始向下滑动。（句中的on which不能换成where，否则意思不明确）
This I did at nine o’clock, after which I sat reading the paper. 九点钟时我做这事，之后我坐着看报。（句中的after which不能换成when，否则意思不明确）
2. 当“介词+which”后面接有被which修饰的名词时，通常不能用关系副词代替。如：
The programme will continue until 1994 by which time $3million will have been spent.
这个项目将持续到1994年。到那时开支将达到300万美元。（句中的by which time不能换成when或where，因为which后跟有它所修饰的名词time）——摘自《限定词与数量词》（外文出版社）
We arrived at noon, by which time the demonstration was over. 我们是中午到的，这时游业已结束。（句中的by which time不能换成when或where，因为which后跟有它所修饰的名词time）——摘自《英语常用词多用途词典》（金盾出版社）
3. 当“介词+which”并不表示时间、地点或原因时，自然不能换成关系副词。
There are three principal routes by which one can drive to North Wales. 开车到北威尔士，有3条主要路线可走。（句中的by which不能换成when或where，因为这里的by which并不表示时间或地点，介词by在此表示“通过”）——摘自《英语常用词多用途词典》（金盾出版社）
This is a subject about which we might argue for a long while. 这是一个我们可能长时间争论的`问题。（句中的about which不能换成when或where，因为这里的about which并不表示时间或地点，介词about在此表示“关于”，所涉及的搭配是argue about）——摘自《张道真英语语法
4、在表语从句和状语从句中不能互换
1.在表语从句中
Is this hotel ______ you said we were to stay in your letter？.
A. that B. where C. the one D. in which
此题可改为：This hotel is where you said we were to stay in your letter．实际上是由where引导的表语从句，答案为B项。
2.在状语从句中
We had better put the bottle of dleeping pills__kids can not find it in case they mistake the pills for candies.此句中“where”并非引导定语从句，而是引导地点状语从句，故不能用"in which".
若用"in which",那句子就变成了定语从句，
in which kids can not find...
= in the sleeping pill kids can not find...
句子就无法理解通了。
3.当定语从句带有不定式时，只能用prep.+which
如，I want a pen with which to write.
I live in a house in which to spend my rest life.
不能用 I live in a house where to spend my rest life.
一、which前面有逗号，逗号前面是个名词，which就近指代那个名词。
（1） Tankfield emailed Pea some photos, which did not cheer Pea up.
which就近指代photos，定语从句中谓语动词did not cheer (Pea up)的发出者即从句主语即先行词photos，是photos没让豌豆家属高兴起来。
（2） Tankfield emailed Pea some photos, which Pea did not find interesting.
which就近指代photos，photos是定语从句中的宾语，把定语从句还原成一个完整句就是Pea did not find the photos interesting.
可以看到，上面两个句子都可以以that为关系代词改写，即
(1)Tankfield emailed Pea some photos that did not cheer Pea up.
(2)Tankfield emailed Pea some photos that Pea did not find interesting.
改写与原版区别在哪儿？就在一个逗号。which前面是名词，名词和which之间没逗号的，在GMAT语法里算错。
二、which前面是介词，介词前面是名词，which就近指代介词前的那个名词，名词和介词之间有无逗号均可。
Tankfield once lent Pea a book from which Pea glimpsed the basics of genes.
这个句子可以“拆”成如下两句：（每个定语从句都可以拆成两句，以先行词为拆分点）
(1)Tankfield once lent Pea a book.
(2)Pea glimpsed the basics of genes from the book.
先行词实际上是定语从句中介词的宾语，这时，需要把介词提前，避免如下表达：
(1)Tankfield once lent Pea a book, which Pea glimpsed the basics of genes from. (XXX)
(2)Tankfield once lent Pea a book that Pea glimpsed the basics of genes from. (XXX)
上中学的时候学过，which引导的定语从句叫“非限制性定语从句”，是不是？它怎么就“非限制性”了？回顾上述GMAT语法规定which有且仅有的两种用法，which指的都是就近的名词，从句其实还是限制性的。
所谓非限制性呢，是说which指逗号之前一套主谓所描述的情况，以逗号前的一个完整句为先行词。比如：
(1)Tankfield might never care to say Happy Birthday to Pea, which was rather sad.
(2)Tankfield might never care to say Happy Birthday to Pea, which Pea did not refuse to acknowledge to herself any more.
注意，这样的非限制性定语从句在GMAT语法中是不成立的，关于which，GMAT语法考试只认可上述两种限制性用法。那么，在GMAT语法考试规则范围内，用什么方法能够表达出原来学过的非限制性定语从句的意思来呢？
分成两句或做出同位语来都是可以的，当然，需要先找出一个名词把原来非限制性定语从句的先行词（即那个完整的句子）概括出来。
一、分成两句
Tankfield might never care to say Happy Birthday to Pea. The fact was rather sad.
Tankfield might never care to say Happy Birthday to Pea. Pea did not refuse to acknowledge the fact to herself any more.
二、做同位语
Tankfield might never care to say Happy Birthday to Pea, the fact, rather sad,beingwhat Pea did not refuse to acknowledge to herself any more.
考题及答案解析：
[考题1]
Youcanfindwhateveryouneedattheshoppingcentre,____isalwaysbusyattheweekend.
A.thatB.whereC.whatD.which
[答案]D
[解析]引导一个非限定性定语从句修饰theshoppingcentre，应选用D选项中的关系代词which，which在该定语从句中充当主语。
[考题2]
York,____lastyear,isaniceoldcity.（2003北京）
A.thatIvisitedB.whichIvisited
C.whereIvisitedD.inwhichIvisited
[答案]B
[解析]引导一个非限定性定语从句修饰York，在定语从句中充当及物动词visit的宾语，应选用B选项中的关系代词which。
[考题3]
Hepaidtheboy$10forwashingtenwindows,mostof____hadn’tbeencleanedforatleastayear.
A.theseB.thoseC.thatD.which
[答案]D
[解析]引导一个非限定性定语从句修饰windows，在定语从句中充当介词of的宾语，应选用D选项中的关系代词which。
[考题4]
Theownerofthecinemaneededtomakealotofimprovementsandemploymorepeopletokeepitrunning,____meantspendingtensofthousandsofpounds.（2006江苏）
A.whoB.thatC.asD.which
[答案]D
[解析]引导一个非限定性定语从句修饰整个主句“theownerofthecinemaneededtomakealotofimprovementsandemploymorepeopletokeepitrunning”所表示的情况，应选用C选项中的`关系代词which，在该定语从句中充当主语。
[考题5]
Dorothywasalwaysspeakinghighlyofherroleintheplay,____,ofcourse,madetheothersunhappy.
A.whoB.whichC.thisD.what
[答案]B
[解析]引导一个非限定性定语从句修饰整个主句“Dorothywasalwaysspeakinghighlyofherroleintheplay”所表示的情况，应选用B选项中的关系代词which，在该定语从句中充当主语。
[考题6]
Theresultoftheexperimentwasverygood,____wehadn’texpected.
A.when B.thatC.whichD.what
[答案]C
[解析]引导一个非限定性定语从句修饰整个主句“theresultoftheexperimentwasverygood”所表示的情况，应选用C选项中的关系代词which，在该定语从句中充当及物动词expect的宾语。
[考题7]
TheEnglishplay____mystudentsactedattheNewYear’spartywasagreatsuccess.
A.forwhichB.atw
[答案]C
[解析]表示“在英语剧中”应用介词in，因此在修饰先行词play的限定性定语从句中也应用介词in与指代先行词play的关系代词which连用，本题只能选C。注意：本题中which充当置于定语从句中最前面的介词in的宾语（inwhich在整个定语从句中充当状语）。
[考题8]
Isawawomanrunningtowardmeinthedark.BeforeIcouldrecognizewhoshewas,shehadrunbackinthedirection____shehadcome.
A.ofwhichB.bywhichC.inwhichD.fromwhich
[答案]D
[解析]表示“从他来的方向跑回去”，应选用介词from。下划线处是引导修饰direction的定语从句。
[考题9]
Frank’sdreamwastohavehisownshop____toproducetheworkingsofhisownhands.
A.thatB.inwhichC.bywhichD.how
[答案]B
[解析]题干句意为：Frank的梦想是拥有一家可以生产自己的手工制品的商店。inwhich相当于intheshop的含义，最适合引导定语从句。
[考题10]
Iwasgiventhreebooksoncooking,thefirst____Ireallyenjoyed.
A.ofthatB.ofwhichC.thatD.which
[答案]B
[解析]ofwhich表示thefirstofthreebooks的含义，介词of不可以省略，that不可以紧跟介词后引导定语从句，因此应选B。
[考题11]
Hewaseducatedatalocalgrammarschool,____hewentontoCambridge.
A.fromwhichB.afterthatC.afterwhichD.fromthis
[答案]C
[解析]this不能引导定语从句修饰前面的school，介词后的关系代词不能是that（“考点72：that引导的定语从句的用法”中将有此考点的具体介绍），因此应排除选项B和D;由于此处which指代前面整个主句，全句意为“他在当地的一所语法学校接受教育之后，又去了剑桥。”，介词应选用after，因此应进一步排除选项A而选出C。
附：定语从句中的that和which用法区别
1、先行若是不定代，that就把which踹
春雨惊春清谷天，夏满芒夏暑相连，秋处露秋寒霜降，冬雪雪冬小大寒。上半年是六廿一，下半年来八廿三，每月两节日期定，最多相差一二天。当先行词为anything, everything, nothing, all, any, much, many, one等不定代词时，只能使用“that”， 不用“which”。
例：Is there anything that I can do for you? 我能给你做点什么吗？
2、先行词前有两数，就用that定无误
当先行词是基数词或序数词修饰时，只能使用“that”， 不用“which”。
例句：
That is the second time that I have been to Japan.
那是我去日本的第二次。
The two buildings that lay on the River Thames fell down last week.
坐落在泰晤士河岸边的那两座大楼上星期倒塌了。
3、先行词前最高级，还用that必无疑
当先行词是形容词最高级或被形容词最高级修饰时，只能使用“that”， 不用“which”。
例句：
This is the most wonderful time that I have ever had.
这是我度过的最美好的时光。
4、句中若有there be, that应把which替
例：
There is no evidence that animals possess a mysterious sixth-sense allowing them to predict natural disasters.
说动物拥有神秘的第六感，可以预知自然灾害，这是没有根据的。
5、先行主中做表语，避免重复从句里
例句：
1）This is not the hospital that it used to be.
这已经不再是以前那座医院了。
2）Mr Thomson is not the man that he was.
汤姆森先生已经不再是以前的他了。
解析：定语从句的先行词均在主句中做表语。
例句：
Which is the course that we are to take ？
我们要学哪门课？
解析：句中已有which,后面不再用which,避免重复用that。
6、先行词前有just/the only/very/same/last等词，关系代词用that,不用which
例句：
1) The North Pole is the only place that you can see polar bears.
北极是唯一能见到北极熊的地方。
2）This is the same bike that he lost.
这就是他丢了的那辆自行车。
注意区分：
3) This is the same bike as he lost.
这辆自行车和他丢的那辆一样。（但不是）
This is the pen which was given by my friend.
先行词 指物代替先行词在定语从句中充当主语
This is the hotel in which you will stay.
(2) 如有两个定语从句，其中一句的关系代词是that,另一句宜于用which.
Let me show you the novel that I borrowed from the liberary which was newly open (新开放) to us.
注意2that \which在代物时常常可以通用，但有时只宜于用that ,不用which.
(1) 先行词是形容词最高级或者它的前面有形容词最高级时
This is the best that has been used against air pollution(反对空气污染) in cities.
English is the most difficult subject that you will learn during these years.
(2) 先行词是序数词，或它的前面有一个序数词时
He is the last person that I want to see.
(3) 主句中已有疑问词时
Which is the bike that you lost?
(4) 先行词既有人又有物时
The bike and its rider that had run over (撞倒了)an old man were taken to the police station.
(5) 先行词是all,much,little,something,everything,anything,nothing,none,the one等代词时
You should hand in all that you have.
We haven’t got much that we can offer you.
I mean the one that you talked about just now.
(6) 先行词前面有only,any,few,little,no,all,one of,the same,the very等词修饰时
The only thing that we can do is to give you some money.
Li Ming is the only one that got full marks (满分)in our class.
Li Ming is one of the students that want to be teachers in our class.
(7) 有两个定语从句，其中一个关系代词已用which,另外一个宜用that
Edison built up a factory(办了一个工厂) which produced things that had never been seen before.
定语从句的关系副词 Where的用法：若先行词指地点且其在定语从句中充当地点状语。
This is the house+I was born in the house.(=I was born there)
介词短语 副词
=This is the house where I was born.这就是我在那儿出生的房子。
先行词 关系副词
in which I was born.
介词+关系代词
which I was born in.
关系代词
这里作介宾的which和that可以省略
that I was born in
1、 当先行词为all, much, little, none及由any, every, some, no所构成的复合不定代词时。
如：
Please tell me anything that you know about the matter.
有关此事，凡是你所知道的请告诉我。
2、 当先行词被any, few, little, no, all, much, some等词修饰时。
如：You can take any seat that is free.
任何空着的座位你都可以坐。
3、 当先行词为序数词或被序数词所修饰时。
如：
This is the fourth film that has been shown in our school this term.
这是我们校本学期放映的第四部电影。
4、 当先行词为形容词最高级或被形容词最高级修饰时。
如：
This is the most interesting story book that I have ever read.
这是我读过的一本最有趣的故事书。
5、 当先行词被the very, the only, the last, the just, the same等修饰时。
如：
The only thing that we could do was to wait.
我们唯一能做的事就是等待。
注意：先行词被the same修饰时，关系代词也可用as。
如：I need the same book that / as you have.
我需要有你一样的书。
6、 当先行词既包含人又包含物时。
如： They are talking of the heroines and their deeds that interest them.
他们正在谈论他们感兴趣的女英雄及她们的事迹。
7、 当先行词是疑问代词who，which，what或主句以这些词开头时。
如：
Who that has ever worked together with him doesn’t admire him?
曾经和他一起工作过的谁不钦佩他？
8、 当先行词为主句表语或关系代词为从句表语时。
如：
Our school is no longer the place that it used to be.
我们的学校现在已不是过去的那个样子了。
9、 先行词为time时，当time表示次数，引导词用that, 可省略。 当表示时间，可用that或when引导，都可省略。
如：
I did't remember the exact time （when/that） I arrived in Shanghai last month.
我不记得上个月到达上海的确切时间了。
最后，请注意以下几种只能使用which的情况:
1、 在“介词＋关系代词”结构中，关系代词必须用which。
如：
This is the reference book of which the teacher is speaking.
这就是老师正在谈及的那本参考书。
注意： 如果介词不放在修饰事物的限定性定语从句的句首， which就可换为that，例如：
This is the question which/that we’ve had so much discussion about. =This is the question about which we’ve had so much discussion.
这就是我们已经多次讨论过的问题。
2、 先行词为“those＋表事物的复数名词”时， 关系代词通常只用which而不用that。
如：You should grasp well those skills which may be used in the future work.
你应该掌握好这些可以用到未来工作中的技能。
最后，记得这个特殊情况吧：当先行词是表示原因或方式的名词时，可以用that引导定语从句，相当于介词+which，that可以省略。
如：
He didn’t like the way that （=in which） she speaks to his mother.
他不喜欢她对他的母亲那样说话。
Imagine the speed that （=at which） he drives the car.
很难想象，他开车开得那么快。
that和which在从句里都可以做宾语和主语，做宾语时可以省略。在定语从句中，有种说法叫"关宾省"，意思是关系代词在限制性定语从句中作宾语可以省略，不管是that，which，还是whom。但是which能引导非限制性定语从句，that则不行。
其次，记得以下只能用that的几种情况：
1. 当先行词为all, much, little, none及由any, every, some, no所构成的复合不定代词时。
如：
Please tell me anything that you know about the matter.
有关此事，凡是你所知道的请告诉我。
2. 当先行词被any, few, little, no, all, much, some等词修饰时。
如：You can take any seat that is free.
任何空着的座位你都可以坐。
3. 当先行词为序数词或被序数词所修饰时。
如：
This is the fourth film that has been shown in our school this term.
这是我们校本学期放映的第四部电影。
4. 当先行词为形容词最高级或被形容词最高级修饰时。
如：
This is the most interesting story book that I have ever read.
这是我读过的一本最有趣的故事书。
5. 当先行词被the very, the only, the last, the just, the same等修饰时。
如：
The only thing that we could do was to wait.
我们唯一能做的事就是等待。
注意：先行词被the same修饰时，关系代词也可用as。
如：I need the same book that / as you have.
我需要有你一样的书。
6. 当先行词既包含人又包含物时。
如： They are talking of the heroines and their deeds that interest them.
他们正在谈论他们感兴趣的女英雄及她们的事迹。
7. 当先行词是疑问代词who，which，what或主句以这些词开头时。
如：
Who that has ever worked together with him doesn’t admire him?
曾经和他一起工作过的谁不钦佩他？
8. 当先行词为主句表语或关系代词为从句表语时。
如：
Our school is no longer the place that it used to be.
我们的学校现在已不是过去的那个样子了。
9. 先行词为time时，当time表示次数，引导词用that, 可省略。 当表示时间，可用that或when引导，都可省略。
如：
I did't remember the exact time (when/that) I arrived in Shanghai last month.
我不记得上个月到达上海的确切时间了。
最后，请注意以下几种只能使用which的情况：
1. 在“介词+关系代词”结构中，关系代词必须用which。
如：
This is the reference book of which the teacher is speaking.
这就是老师正在谈及的那本参考书。
注意： 如果介词不放在修饰事物的限定性定语从句的句首， which就可换为that， 例如：
This is the question which/that we’ve had so much discussion about. =This is the question about which we’ve had so much discussion.
这就是我们已经多次讨论过的问题。
2. 先行词为“those+表事物的复数名词”时， 关系代词通常只用which而不用that。
如：You should grasp well those skills which may be used in the future work.
你应该掌握好这些可以用到未来工作中的技能。
最后，记得这个特殊情况吧：当先行词是表示原因或方式的名词时，可以用that引导定语从句，相当于介词+which，that可以省略。
如：
He didn’t like the way that (=in which) she speaks to his mother.
他不喜欢她对他的母亲那样说话。
Imagine the speed that (=at which) he drives the car.
很难想象，他开车开得那么快。
1.He lived on an invalidity pension which came as a weekly giro.
他靠每周领取的作为病残养老金的直接转账救济支票过日子。
2.Politicians want a lap-dog press which will uncritically report their propaganda.
政客们想要的是不问是非、甘为他们搞宣传的哈巴狗一样的新闻媒体。
3.We were in the same college, which was male-only at that time.
我们那时在同一所学院，当时只招男生。
1、在后置的非限制性定语从句中代替上文出现的事物或情况(单数或复数)。
2、在问句中作为疑问代词，在名词从句中作为连接代词用，其含义为“哪个、哪些”。
3、如果非限制性定语从句的先行词不是指主句内容，而是指具体的人、时间、地点，则不用which。
一、关系代词that 和which 在定语从句中作主语和宾语，放在先行词和定语从句之间，起联系作用。指物时，一般情况下可互换。如： Here is the pen that/which you lost yesterday.(that/which 指物作宾语) A plane is a machine that/which can fly.(that/which 指物，作主语) He is the most careful boy that I know.(that 指人，作宾语) The man that works in this room is a chemist.(that 指人，作主语)
二、that,which 在从句中作主语时，不能省略。作宾语时在口语中和非正式问题中经常省略。如上例1 和中的that,which 都可省略。
三、关系代词在主语从句中作主语时，从句的谓语动词的人称和数须和先行词一致。 Wheat is a plant that/which is grown in the north of China.
四、在定语从句中，关系代词that 和which 指物时，一般没有区别，但下列几种情况中不能互换：
只能用that 的情况：
a)先行词为 all,everything,nothing,anything,little 等不定代词时(something 后也可用which)： Is there anything (that) I can do for you in town? That’s all (that) I know.
b) 先行词被序数词所修饰时： The first thing (that) we should do is to work out a plan.
c) 先行词被形容词最高级所修饰时： This is one of the most exciting football games (that) I have ever seen. The nanjing yangtse river bridge is the longest bridge (that) they have ever seen.
d) 先行词 被only,very,no,any,same,little,one of 等词所修饰时： This is the only thing (that) we can do now. He gave me the same pen (that) he borrowed from me. Do you have any books that were written by Lu Xun? This is the very book (that) I want to read.
e) 当先行词中既有人又有物时： The man and the car (that) you want to see are all here. 你相见的人和车都在这里。
f) that 可指人，which 则不能： Who is the man that is reading the newspaper over there?
g) 在 “the time when”等结构和某些时间状语中，when 常被that 代替，而且that 往往省略： I may leave here any time I want to. During the time I was there I visited him twice.
h)way 后面可根由that 引导的定语从句，但that 一般都省略： That was the way she looked after us.
在下列情况中，只能用which:
a) 放在介词后面做介词宾语时： This is the question about which we’ve had so much discussion. 但是，如把介词放在从句的后部，这时which 就可换为that 并常省略。如上例可改为： This is the question (that) we’ve had so much discussion about.
b) 在非限制性定语从句，无论指物指人，都不能用that。指物时，只能用which 和其他关系代词。如： All the books there,which have beautiful pictures in them,were written by him.
我们知道，as和which作为关系代词都可以用来引导非限制性定语从句，指代整个主句所表达的内容，在从句中作主语或宾语，但它们在用法上有区别，这一点许多学生往往搞不清楚。现就它们引导非限制性定语从句的用法简述如下：
一、相同之处
当从句位于主句之后，引导词指代整个主句所表达的全部意义时，as和which可以互换。如：
The elephant is like a snake,as/which everybody can see.
大家都看得出，这头大象像条蛇。
A big earthquake occurred there last night,as/which was reported on TV.
据电视报道，昨夜那里发生了大地震。
She is from Shanghai,as/which I know from her accent.
她来自上海，那是我从她的口音知道的。
二、不同之处
1、as引导非限制性定语从句时，位置比较灵活，可位于主句之前，也可位于主句之中或之后；而which引导非限制定语从句只能位于主句之后，不能位于主句之前。如：
_______ is known to everybody,the moon travels round the earth.
A.It B.As C.That D.Which
答案：B
_______ is mentioned above,the number of the students in senior high schools is increasing.
A.Which B.As C.That D.It
答案：B
Air,as we know,is a gas.众所周知，空气是一种气体。
He is very careful,as his work shows.
他的工作表现表明他非常谨慎。
as引导非限制性定语从句常有“如同。.。.。.那样”的含义，因此在一些固定结构中，如：
as we know;as is known to all（众所周知）
as we all can see（正如我们大家都能看到的那样）
as has been said before/above（正如前面所述）
as has been pointed out（正如所指出的那样）
as might be imagined（可以想象得到）
as might be expected（正如所预料的那样）
as is often the case（情况通常是这样）
以上种种固定搭配，一般不能用which代替as。
2、搭配上，在由the same或such所修饰的名词后通常用as作关系代词引出非限制性定语从句。如：
I have got into the same trouble as he (has)。
我遇到了与他一样的麻烦。
I've never heard of such a moving story as he is telling.
我从未听过像他讲得那么有趣的故事。
3、which引导的从句在意义上相当于一个并列句，可以用and this代替，意思是“这件事”；as引导的从句主要起连接上下文的作用，表达说话人的观点、看法，并指出主句内容的根据或出处等。如：
He sold his new car,which surprised me.
=He sold his new car,and this serprised me.
Einstein,as we know,is a famous scientist.
我们都知道，爱因斯坦是一位著名的科学家。
As is known to all,Taiwan is part of China.
众所周知，台湾是中国的一部分。
4、当which在从句中指代的是先行词本身而不是主句时，不可用as代替which。如：
The peach tree,which I planted last year,has not borne any fruit.
这棵桃树是我去年种下的，还没有结出任何果实。
The book,which I bought yesterday,is very instructive.
我昨天买的这本书很有教育意义。
5、在从句中作主语时，which既可作系动词be的主语，也可作实义动词的主语，而as只可作系动词be的主语。如：
He married her,which was nature.（可用as代替which）
他和她结婚了，这是很自然的事。
She met the boy,which delighted her.（不可用as代替which）
她见到了那个男孩，这使得她很高兴。
He failed in the exam again,which made his parents very angry.
他考试有不及格了，这是他父母很生气。
6、as引导的从句在意义上不可与主语相悖，而which引导的从句则不受此限制。
Mum treats me like a baby,which I can't bear.
妈妈把我当小孩看待，这是我不能忍受的。