说明：关系代词that和关系副词why不能引导非限制性定语从句。

4. 限制性定语从句中只能用that 引导定语从句的情况

1) 当先行词是everything, anything, nothing (something 除外), all, none, few, little, some等代词时，或当先行词受every, any, all, some, no, little, few, much等代词修饰时。如：

Have you taken down everything that Mr. Li said? 李老师讲的你都记下来了吗?

There seems to be nothing that is impossible to him in the world. 对他来说似乎世界上没有什么不可能的事。

2) 当先行词被序数词修饰时。如：

The first place that they visited in London was the Big Ben. 在伦敦他们参观的第一个地方是大本钟。

3) 当先行词被形容词最高级修饰时。如：

This is the best film that I have ever seen. 这是我看过的最好的电影。

4) 当先行词被the very, the only修饰时。如：

This is the very dictionary that I want to buy. 这正是我要买的词典。

After the fire in his house, the old car is the only thing that he owns. 家里发生了火灾过后，那辆旧车成了他的唯一拥有。

注意：当先行词指人时，偶尔也可用关系代词who。如：

Wang Hua is the only person in our school who will attend the meeting. 王华是我校唯一出席会议的人。

5) 当先行词前面有who, which等疑问代词时。如：

Who is the man that is standing by the gate? 站在门口的那个人是谁?

Which is the T-shirt that fits me most? 哪件T恤衫最合我的身?

6) 当先行词为人与动物或人与物时。如：

They talked about the persons and things that they remembered at school 他们谈论着他们所能记起的在校时的人和事。

Look at the man and his donkey that are walking up the street.　瞧瞧那个沿街走来的人和他的毛驴。

五、as, which 非限定性定语从句

由as, which 引导的非限定性定语从句，as和which可代整个主句，相当于and this或and that。As一般放在句首，which在句中。例如：

As we know, smoking is harmful to one’ s health. 如我们所知，吸烟有害健康。

The sun heats the earth, which is very important to us. 太阳使地球暖起来，这对我们人类很重要。

as可引导非限制性从句，常带有“正如”的意思。

As we know, smoking is harmful to one’ s health. 如我们所知，吸烟有害健康。(as作know的宾语)

As is known, smoking is harmful to one’ s health. (as作从句的主语，谓语动词know要用被动式。)

六、关系代词与关系副词的选择

用关系代词还是关系副词引导定语从句主要看关系词在定语从句中的作用(即所担当的句子成分)。试比较：

A. I know a place where we can have a picnic. 我知道一个我们可以野炊的地方。

I know a place which / that is famous for its beautiful natural scenery. 我知道一个以自然景色优美而闻名的地方。

B. I'll never forget the days when I worked together with you. 我永远忘不了我们一起工作的日子。

I will never forget the days that / which we spent together. 我永远忘不了我们一起度过的日子。

C. This is the reason why he was dismissed. 这就是他被解雇的原因。

This is the reason that / which he explained to me for his not attending the meeting. 这就是他向我解释的他没有参加会议的原因。

以上就是高三英语语法知识点定语从句，希望能帮助到大家。