定语从句分几种.
1.关系代词引导的定语从句
在下面几种情况下必须用关系代词that引导定语从句:
(1) 先行词是不定代词all ,few,little,everthing ,nothing anyting,none等.如：
Is there anything that you want to buy in the shop?
你在商店里有什么东西要买吗?
(2) 先行词被序数词或形容词最高级所修饰,或本身是序数词、基数词、形容词最高级.如：
This is the best movie I’ve ever seen.
这是我看到过的最好的一部电影.
(3) 先行词被all, any ,every ,each, few,little, no ,some等修饰时.如：
I have read all the books(that )you gave me.我读了你给我的所有的书.
(4) 先行词被the only , the every ,the same, the last 修饰时.如：
He is the only person that I want to talk to .
他就是我要谈话的那个人.
(5) 当并列的两个先行词分别表示人和物时.如：
They are talking about thins and persons that they remembered.
他们在谈论他们所能回忆起来的人和事.
(6) 为避免重复,在以who或which开头的特殊疑问句中.如：
Who is the girl that is crying ?正在哭泣的那个女孩是谁?
Which of the books that borrowed from the library is yours
从图书馆借的哪一本书是你的?
(7) 用作关系代词,修饰表示时间的名词如day, time , moment 代替when .如：
It happened on the day that/when he was born
这事碰巧发生在他出生的那天.
(8) 如果有两个定语从句,其中一个关系词已用which则另一个用that .如：
The country built up a factory which produced things that have never been seen before.
这个国家建立了一个工厂,生产以前未曾见到过的东西.
(9) 主句以there be开头.如：
This is a seat in the corner that is still free.那个角落还有个座位空着.
2. 限制性定语从句
(1) who引导的限制性定语从句
关系代词who用于指人,通常在句中作主语.在非正式文体中,who可以代替whom在句中作动词宾语和介词宾语,而且常常省略.在作介词宾语时,不能位于介词之后.如：
A doctor is a person who looks after people?蒺s health.
医生是关照人们健康的人.
Nobody who understands the subject would say such a thing.
懂这一行的人是不会说这样的话的.
The man who I saw is called Smith. 我见到的那个人名叫史密斯.
There’s no one works harder than you. 没有比你更用功的人了.
(no one后省去了用作 主语的who)
(2) whom引导的限制性定语从句
The gentleman whom she encountered addressed her with courtesy.
她相遇的那位先生很有礼貌地和她讲话.
I have just met a lady (whom) I saw last week.
我刚遇到一位我上个星期见过的贵妇人.
关系代词whom用于指人,是who的宾格形式,在从句中作动词宾语或介词宾语,常常省略.whom作介词宾语时,介词可位于whom之前或句末,在非正式文体中常位于句末；紧接介词的whom不能省略.
He wanted to find someone with whom he could discuss books and music.
他想找个能共同研讨书和音乐的人.
This is the teacher (whom) we have talked about.
这就是我们谈论过的那个老师.
(3) whose引导的限制性定语从句
whose是关系代词who的所有格形式,在从句中作定语.whose通常指人,也可指动物或无生命的事物：
An electromagnet is a device whose magnetism is produced by an electric magnet.
电磁铁是一种由充电的磁铁产生磁力的装置.
You're the only one whose advice he might listen to.
只有你的话他可能会听.
I'd like a room whose window looks out over the sea.
我想要一个窗户面临大海的房间.
(4) which引导的限制性定语从句
She was not on the train which arrived just now.
她不在刚才到达的那列火车上.
关系代词which在从句中作主语或介词宾语,作宾语时常常省略.which作介词宾语时,介词可位于是which之前或句末,在非正式文体中常位于句末；紧接介词的which不能省略.
which主要用于指无生命的事物,除此之外,还可指婴儿、动物、以及某些表示单数意义的集体名词.
(5) 关系代词that引导的限制性定语从句
关系代词that既可指人,又可指物.它在从句中可以作主语、动词宾语、介词宾语和表语.that作动词宾语或介词宾语时常常省略.在作介词宾语时,介词须位于句末,而不能位于that之前.
Water that is impure often causes serious illness.
水不洁常会引起重病.
Fanny,bring the water and put it down in the middle of the room,lazy creature that you are.
范妮,拿水来,放在屋子当中,你这懒鬼.
(6) when等引导的限制性定语从句
关系副词when指代和修饰主句中表示时间的先行词,在从句中作时间状语,可以省略.在语义上,when相当于“介词+which”.如：
July and August are the months when the weather is hot.
七八月是天气很热的月份.
Every hour since I came has been most enjoyable.
我来之后的每一个小时都是非常好玩的.
On the day before we left home there came a snow storm.
在我们离家的前一天,下了一场暴风雪.
(7) where引导的限制性定语从句
关系副词where指代和修饰主句中表示地点的先行词,在从句中作地点状语,当先行词为place时,where可以省略.在语义上,where相当于“介词+which”：
The knee is the joint where(=at which)the thigh bone meets the large bone of the lower leg.
膝盖是大腿骨和小腿大骨相连处的关节.
She’s going home where she can rest.
她要回家了,在家里她可以休息.
A stone marks the spot where the treaty was signed.
有一块石头标着那个签订条约的地方.
(8) why引导的限制性定语从句
关系副词why的先行词只有reason, 在从句中作原因状语,可以省略：
The reason why he left is not convincing.
他离开的理由无法令人信服.
There was no definite reason why she should do so.
她这样做并没有什么一定的理由.
(9) 关系代词as引导的限制性定语从句
关系代词as既可指人,又可指物,在从句中作主语、宾语、状语或表语.其具体用法如下：
① as与the same连用：
This is the same computer as I have bought.
这台计算机和我买的那台一样.（as作宾语）
I’ll do the experiment the same way as he does.
我将采用和他同样的方法做这个实验.(as作方式状语)
he studies in the same college as I do.
他和我在同一所大学学习.(as作地点状语)
② as与such连用：
They returned with coffee,wine,and such provisions as were needed.
他们带着咖啡、葡萄酒以及所需的给养回来了.（主语）
here are such questions as are of ten asked by the college students.
这是些大学生们常常问的那类问题.（as作主语）
I have never seen such kind of girl as she is.
我从未见过像她这样的女孩.（as作表语）
he didn’t believe such reason as she did so.
他不相信她那样做的理由. （as作原因状语）
③ as与as连用：
There is as good fish in the sea as ever came out of it.
海里有的是鱼（天涯何处无芳草）.（主语）
She tried to make as few mistakes as she could avoid.
她尽可能地避免犯错误.（动词宾语）
④ as与so连用：
He can tell so interesting a story as moves us to tears.
他能讲把我们感动得流泪的故事.（主语）
Here is so big a stone as no one can lift.
这是一块没人能搬得动的大石头.（动词宾语）
(10) “介词+关系代词”引导的限制性定语从句
在介词后引导限制性定语从句的关系代词为whom, whose和which,介词的选择取决于它与先行词的搭配或与从句中谓语动词的搭配：
The family at whose house we stayed were friends of my father?s. 我们曾住过的那家的主人是我父亲的朋友.
This is the book for which you asked. 这是你所要的书.
The official to whom we applied for a permit was most obliging.
我们向他申请许可证的那位官员非常热情.