★从句用作关系代词叫关系代词从句。常用that , wh。引导，修饰主句中的名词或代词。
This is the book that you are looking for.
( you are looking for是关系代词从句，修饰前面的名词book)
In America Mother's Day started quite differently from the way it started in Britain.
( it started in Britain是关系代词从句，修饰前面的名词way )
POINT 1 that引导从句的用法
The only language (that) I know well is English.
The language is English. I know the language well.(language作know的宾语)
That's one thing (that) I haven't forgotten today!
Larry found the pen that he had lost.
The man that came first today is Mike.
Wheat is a plant that is grown in mid-west America.
The house that stands on the hi川s mine.
( that stands on the hill是关系代词从句，修饰house，that在
POINT 2 who引导从句的用法
The man who came first today is Mike.
The young man who came to see her is her brother.
He's the man who/that lives in the next room.
错：I know where does she live.
对：I know where she lives.
错：He said that he is playing soccer at that time.
对：He said that he was playing soccer at that time.
she is a teacher.
she will come back in two days.
she has just finished it.
she went to Taiwan two days ago.
He asked me+
what I wanted.
where I was going.
when I would leave.
why I had come here
错：The teacher said that the earth was round.
对：The teacher said that the earth is round.
The teacher said the sun rises in the east and sets in the west.
The teacher told us the earth is one of the sun's planets.
错：I think your answer isn't right.
对：I don't think your answer is right.
当宾语从句表示否定之意，且主句中主语是I，动词为think, believe等时， 习惯上是将否定移转.使主句成为否定式.而从句使用肯定式。
错：I don't think you are a teacher, do I?
错：I don't think you are a teacher, aren't you?
对：I don't think you are a teacher, are you?
错：They are talking about if Mr. Green can speak Chinese.
对：They are talking about whether Mr. Green can speak Chinese.
错：I will tell him the good news as soon as he will come back.
对：I will tell him the good news as soon as he comes back.
在由when, before , after，as soon as等引导的时ie}状语从句中，如果主句 的动词是一般将来时.从句中的动词用一般现在时代替将来时。
错：一Why didn't he come to school?一For he was ill.
对：一Why didn't he come to school?一Because he was ill.
错：You'll be late for class if you won't hurry up.
对：You'll be late for class if you don't hurry up.
错：While my friend came yesterday, I was busy doing my homework.
对：When my friend came yesterday, I was busy doing my homework.
错：He went to bed until he finished his homework.
对：He didn't go to bed until he finished his homework.
错：He was too angry that he couldn't speak.
对：He was so angry that he couldn't speak.
对：He was too angry to speak.
错：I don't know if he comes.
对：I don't know if he will come.
错：This room is more bigger than that one.
错：This room is very bigger than that one.
对：This room is much bigger than that one.
在形容词或副词比较级前不能用very，更不能用more剩多饰，可用much even·a little等来修饰。