英语不止做为一门语言和交流工具，而是被提升到了必备技能的范畴，精品小编准备了高中英语基础知识，具体请看以下内容。

一 定语从句

(一)定语从句概述

1. 定义：修饰一个名词或代词的从句称为定语从句，一般紧跟在它所修饰的先行词后面。2. 先行词：被定语从句修饰的名词或代词称为先行词。3. 关系词：引导定语从句的关联词称为关系词。关系词有关系代词和关系副词。

4. 关系词常有三个作用：引导定语从句;代替先行词;在定语从句中充当一个成分。如： Harry Potter is the most interesting novel that I have read. 解析：that I have read是定语从句;novel是先行词;that 是关系代词，代替先行词novel，在从句中作have read的宾语。 I've become good friends with several of the students in my school ______ I met in the English speech contest last year. A. who B. where C. when D. which解析：首先确定先行词，根据空格后的从句I met in the English speech contest last year缺少met的宾语，该宾语应当为sb.，故可判断先行词不是从句最靠近的my school，而是被in my school所隔开的the students。故此，关系代词该用who/whom或者省略。四个选项中，只有A选项正确。

(二)关系代词使用规则

规则1：关系代词若在限制性定语从句中作宾语并且前面无介词时，关系代词可省略，其他情况不可省。

She is the woman (whom / that/who) I wanted to see yesterday. 规则2：定语从句中的主谓一致问题 (1) 关系代词在定语从句中作主语时，从句谓语动词的人称和数要和先行词保持一致。

I, who am your close friend, will try my best to help you whenever you are in trouble.(2) one of + 复数名词+ 关系代词+ 复数动词;而the only one of + 复数名词+ 关系代词+ 单数动词。

Harry Potter is one of the best­sellers that are popular with teenagers.

Harry Potter is the only one of the best­sellers that makes the author a billionaire. (3) 非限制性定语从句中，由关系代词as或which代替整个主句时，从句谓语动词要用第三人称单数。

Great changes have taken place in China, as is known to all.(4) 关系代词和谓语动词之间有插入语时，谓语动词单复数要看关系代词的指代。

To own a TV set in each family, which we think was impossible 20 years ago, now has become true.规则3：指物时，定语从句中的关系代词只能用that的情况： (1) 当先行词为everything, anything, nothing, the one, none, all, much, few, any, little等不定代词时。

All that can be done has been done. (2) 当先行词被the only, the very, all, much, few, any, little, no修饰时。

This is the very dictionary that I want to buy.(3) 当先行词是序数词、形容词最高级或者先行词被序数词、形容词最高级修饰时。

The first place that they visited in London was the Big Ben.

(4) 先行词既有人又有物时。Can you remember the scientist and his theory that we have learned? (5)当主句的主语是疑问词who或which时，为避免重复要用that。Who is the man that is standing there?(6) 有两个定语从句时，其中一个关系代词已用which，另一个则用that。

They have set up a company, which deals with the things that are related to environment protection.(7) 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，只用that。

Hangzhou is no more the city that it used to be.规则4：指物时，定语从句中的关系代词只能用which的情况： (1) 在引导非限制性定语从句时。

The tree, which is four hundred years old, is very famous here. (2)介词后。We depend on the land from which we get our food.

(3)有两个定语从句时，其中一个关系代词已用that，另一个宜用which。

规则5：指人时，定语从句中的关系代词只能用who的情况：(1)当先行词是anyone, those时。 Is there anyone who is ready to help the injured person? (2)有两个定语从句时，其中一个关系代词已用that，另一个宜用who。

规则6：whose可以指代人或物，在定语从句中作定语， 后跟名词。

指物时，whose+名词=名词+ of which = of which+ 名词。

The classroom whose door/ the door of which/of which the door is broken is on the second floor.规则7：关系代词as和which

在非限制性定语从句中，as和which可代替整个主句，相当于and this或and that。二者的区别主要在于： (1) as引导的非限制性定语从句既可以在主句前，也可以在主句后，有时还可以插入句中，常带有“正如……，正像……”的意思。而which引导的非限制性定语从句只能放在主句之后，翻译成“这”。

As we know, smoking is harmful to one’s health. The man died last night, which is a lie.(2)主句中出现the same, as, such, so修饰先行词或者the same…as, such…as, so…as, as…as 等结构中需选择as 关系代词在定语从句中作主语或宾语。

This house is not such as I expect.(such为代词，作先行词; as在从句中作宾语)

Here is so big a stone as no man can lift. I live in the same building as he (lives in). 【注意】当先行词由the same修饰时，有时也用that引导定语从句，但是和由as所引导的意思不同：that表示同一个，as表示同一类。

The pencil is the same one as I lost last week.

The pencil is the same one that I lost last week (3) 在以下结构中，一般也用as: as (it) appears, as (it) seems likely, as (it) often happens, as (it) was pointed out/said/reported/announced, as (it) was said earlier, as I remember (it), as is well­known, as is known to all, as anybody can see等。As was pointed out, this kind of substance is poisonous.

as 的这种用法通常出现在一些固定短语之中如：

1.as has been said before 如上所述

2.as may be imagined 正如可以想象出来的那样

3.as is well known 众所周知

4.as was expected 正如预料的那样

5.as has been already pointed out 正如已经指出的那样

6.as we all can see 正如我们都会看到的那样规则8：“介词+关系代词”引导的定语从句，关系代词指人时用whom，指物时用which。 (1) 某些带有介词的动词短语，介词可以提至关系代词之前，但是在一些固定搭配的短语动词中，由于动词和介词不可以分割，因此不能将介词置于关系代词之前，如take care of, look for, look after, care for等。

This is the book (which / that) I am looking for.

(2)“介词+关系代词”前可有some, any, none, both, all, neither, most, each, few等代词或者数词，有时数词或代词也可以放在“介词+关系代词”之后。 He loved his parents deeply, both of whom are very kind to him.

= He loved his parents deeply, of whom both are very kind to him.

(3)介词+which / whom+to do结构。这种结构可以改为：介词+which / whom+定语从句。

I don't have enough money with which to buy such an expensive dress.

=I don't have enough money with which I can buy such an expensive dress. (4)在非限制性定语从句中，which可作定语，指先行词(短语或句子)所表示的信息，形成“介词+which +名词”结构，相当于and in/at/during this/that+名词。