1> 关系代词通常用that

1.1> 先行词前有“最高级”

加重语气；

This is the most interesting book that I have ever read.
这本书是我读过最有趣的书。

• 宾格关代，that；

This is the book 【which / that】 I have ever read.
这本是我读过的书。

She is the most beautiful girl that I have ever seen.
她是我曾见过最美的女孩。

1.2> 先行词前有“序数”

He is the last man that I want to see.
他是我最不想遇见的人。

Ayesha is the first girl that talked to me in the class.
Ayesha 是班上第一个跟我说话的女孩。

1.3> 先行词前有 “人+物”

The story is about a boy and his dog that saved our village.
这是关于拯救我们村庄的男孩和他的狗的故事。

I know the old man and the cat that are sitting on the couch.
我认识坐在长沙发上的那位老人和那只猫。

1.4> 先行词前有 “疑问词”

• 避免重复；

Who that really knows him can believe him?
认识他的人有谁能够相信他？

Who is the boy that is playing basketball there?
在那里打篮球的那个男孩是谁？

1.5 > 先行词前有 “all,no,every,any ”

• 强调句型

Every word that he said had a deep meaning in it.
他说过的每一句话都有深意。

• Every word that he said had a deep meaning in it.

All that you have to do now is prepare for the final exam.
我现在所要做的就是准备期末考。

• All you have to do【缺宾语】 now is 【to】prepare for the final exam

• 强调句型: All that S+V … is （to）V…

1.5 > 先行词前有 “the only, the same, the very”

This is the same pencil that I lost yesterday.
这支笔和我昨天丢的那支一样。

• This 【is】 the same pencil 【that】 I 【lost】{缺宾语} yesterday.

• 定语从句分析方法： 找 2动词，1缺失，1先行词；

The only color that I like is yellow.

• The only 【color】that I 【like】{缺宾语}【is】 yellow。

That is the very point that I want to say.
那正是我想说的。

• That 【is】 the very 【point】 I 【want】 to say{缺宾语}.

2> 关系代词不用that

2.1 > 介词之后，关系代词不用that

That is the girl whom I dated with.
That is the girl who I dated with.
That is the girl I dated with.
That is the girl with whom I dated.
那位就是我约会过的女孩。

• That 【is】 the girl 【连词+宾语】I 【dated】 with {缺宾语}.

2.2 > 逗号之后，关系代词不用that

Our teacher, who usually comes on time, arrived late today.
我们老师通常都准时到，今天却迟到了。

My wife, who lives in Paris, has sent me a letter.
我妻子，她住在巴黎，寄了封信给我。