引导定语从句的关系词有关系代词和关系副词,常见的关系代词包括that,which,who，那么，定语从句that用法是？
(1)不用that的情况
(a) 在引导非限定性定语从句时。
(错)The tree, that is four hundred years old, Is very famous here.
(b) 介词后不能用。
We depend on the land from which we get our food.
We depend on the land that/which we get our food from.
(2) 只能用that作为定语从句的关系代词的情况
(a) 在there be 句型中，只用that，不用which。
(b) 在不定代词，如：anything, nothing, the one, all等作先行词时，只用that，不用which。
(c) 先行词有the only, the very,the same,the last,just修饰时，只用that。
(d) 先行词为序数词、数词、形容词最高级时，只用that,不能用which。.
(e) 先行词既有人，又有物时。
(f) 先行词指物，在主句中作表语时.
(g) 为了避免重复.
(h)先行词是the way或the reason时，that可作关系副词，也可省略
(i) 主句的.主语是疑问词who /which时
定语从句that例句
1. He is a good boy. 形容词作定语
2. Two boys need two pens. 数词作定语
3. His son needs Tom's pen. 形容词性物主代词或名词所有格作定语
4. The boy in blue is Tom. 介词短语作定语
e is a woman doctor. 名词作定语
6. The boy there needs a bike. 副词作定语
e is nothing to do today. 不定式作定语
8. The smiling boy needs a friend. 现在分词作定语
9. A boy called Tom saved the girl. 过去分词(短语)作定语
10. He is the man that I met yesterday. 定语从句
定语从句知识
一、定语从句的概念：在复合句中，用作定语的从句叫做定语从句。
二、定语从句的位置：通常位于它所修饰的名词或代词之后。
三、被修饰的名词或代词叫做先行词。
四、引导定语从句的关联词为关系代词和关系副词。关系代词(who, whom, whose, that, which等)在定语从句中可用作主语、定语、宾语等;关系副词(when, where, why等)在定语从句中只用作状语。关系代词和关系副词放在先行词及定语从句之间起连接作用，同时又作定语从句的重要成分。
五、定从基本形式：先行词(名词/代词) + 关系代词/关系副词+ 定从
六、that引导的定语从句
She is the girl that talked to you yesterday. (that作主语)
The coat (that) I put on the desk is blue. (that作宾语)
结论：that引导的定语从句既可以修饰人，也可以修饰物;
that在从句中作主语或宾语;
作主语时不可省略，作宾语可省略。
例如：
1. I like music. I can dance to music.
I like music that I can dance to. (that在从句中用作宾语。)
2. I prefer a sandwich. A sandwich is really delicious.
I prefer a sandwich that is really delicious.(that在从句中用作主语。)
注意：that在定语从句中作主语时，定语从句中谓语动词的单复数应与先行词保持一致.
例如：I prefer movies that are scary.
I like a sandwich that is really delicious.
I love the singer that is beautiful.
I have a friend that plays sports.
