利用句子合并来学习定语从句定语从句两个术语：先行词，关系词先行词：被修饰的名词、名词词组或代词关系词（关系代词或关系副词）：连接先行词与定语从句的词。
关系代词有：who, whom, whose, that, which等；关系副词有：when, where, why等；1、关系词在定语从句中充当主语先行词为人时（1）两个单句为The boys are from Class One. The boys are playing football.（2）第一句为主句，第二句为从句，将两个单句合并为一句。
The boys（the boys are playing football）are from Class One.(3) 括号中句子里的主语the boys, 和先行词是同一个词，应该用关系词替换从句中重复的the boys. The boys 在从句中作主语，关系词中能作主语并代表人的是who, thatThe boys（who\that are playing football）are from Class One.(4) who\that==the boys, 在定语从句中做主语的成分，并连接先行词和定语从句。
先行词为物时（1）I found the letter. The letter came yesterday.（2）I found The letter( the letter came yesterday).（3）用关系词替换从句中重复的the letter, 关系词中能作主语并代表物的是which, thatI found The letter(which\that came yesterday).（4）which\that==the letter, 在定语从句中做主语的成分，并连接先行词和定语从句。
2. 关系词在定语从句中充当宾语先行词为人时（1）The man is my friend. You met the man just now（2）The man (you met the man just now) is my friend.（3）用关系词替换从句中重复的the man, 关系词中能作宾语并代表人的是whom, thatThe man (whom\that you met just now) is my friend.（4）whom\that==the man, 在定语从句中做宾语的成分，并连接先行词和定语从句。
做宾语的关系词whom\that 可以省略The man ( you met just now) is my friend.先行词为物时（1）This is the pen. He bought the pen yesterday.（2）This is the pen (he bought the pen yesterday).（3）用关系词替换从句中重复的the pen, 关系词中能作宾语并代表物的是which, thatThis is the pen (which\that he bought yesterday).（4）which\that==the pen, 在定语从句中做宾语的成分，并连接先行词和定语从句。
做宾语的关系词which\that 可以省略This is the pen (he bought yesterday).3. 关系词在定语从句中充当定语(1) I helped the man. The man’s car was broken.(2) I helped the man (the man’s car was broken).(3) the man’s 是名词所有格，起到定语的作用修饰car, 用关系词替换从句中重复的the man, 关系词中能作定语，表示“谁的”是whoseI helped the man (whose car was broken).(4) whose=the man’s, 在定语从句中做定语，并连接先行词和定语从句。
Whose不但可以表示“谁的”，还可以指物，表示“什么的”。
例如：I once lived in a house. The roof of the house has fallen in.I once lived in a house (the roof of the house has fallen in).I once lived in a house (whose roof has fallen in).此句还可以改为：I once lived in a house (the roof of which has fallen in).I once lived in a house (of which the roof has fallen in).4. 关系词在定语从句中充当状语时时间状语(1) I still remember the day. I first came to the school on the day.(2) I still remember the day (I first came to the school on the day).(3)重复的词是the day, on the day在从句中充当时间状语的成分，关系词中能作时间状语的词是when.I still remember the day (when I first came to the school).(4) when=on the day, 在定语从句中做时间状语，并连接先行词和定语从句。
地点状语(1) The house has been pulled down. I lived in the house ten years ago.(2) The house (I lived in the house ten years ago) has been pulled down.(3)重复的词是the house, in the house在从句中做地点状语的成分，关系词中能作地点状语的词是where. The house (where I lived ten years ago) has been pulled down.(4) where=in the house, 在定语从句中做地点状语，并连接先行词和定语从句。
原因状语(1) The reason is not clear. He refused the invitation for the reason.(2) The reason (he refused the invitation for the reason ) is not clear.(3)重复的词是the reason, for the reason在从句中做原因状语的成分，关系词中能作原因状语的词是why. The reason (why he refused the invitation) is not clear.(4) why=for the reason, 在定语从句中做原因状语，并连接先行词和定语从句。
另外关系副词when, where, why可以改为,介词+which, 介词取决于与先行词的搭配。
例如：I still remember the day (when I first came to the school).== I still remember the day (on which I first came to the school).The house (where I lived ten years ago) has been pulled down.==The house (in which I lived ten years ago) has been pulled down.The reason (why he refused the invitation) is not clear.==The reason (for which he refused the invitation) is not clear.根据关系词在从句中所充当的成分，可总结如下：从句缺主语who, that, 先行词是人从句缺宾语whom, that, who,从句缺定语whose从句缺主语which, that先行词是物 从句缺宾语which, that, 省略 从句缺定语w hose指时间when 指地点 where指原因 why定语从句合并句子例子练习：1.I have a friend. He likes listening to classical music._____________________________________________________________st week Mary wore the dress. I gave it to her._____________________________________________________________3.The girl is from America. Her father is a Chinese._____________________________________________________________4.Do you know the man? The man spoke just now._____________________________________________________________5. Who is the man? He is drawing a picture over there?_____________________________________________________________6.My grandparents live in a house. It is more than 100 years old._____________________________________________________________知识巩固：一、that 和which 用法的区别(1) 先行词为all, everything, nothing, something,anything, little, much 等不定代词时。
I am sure she has something _____ you can borrow.Do you have anything _____ you don’t understand(2)先行词被all, every, no, some, any, little, much 等修饰时。