○3 只能用which的情况：
a． 关系代词前有介词。 This is the house in which we lived last year .
b． 先行词本身是that 。 The clock is that which I bought yesterday .
c． 非限制性定语从句。 His English , which used to be very poor, is now excellent .
○4 定语从句在句中作定语，所以在使用时，相当于现在分词短语，过去分词短语，动词不定式短语，介词短语作后置定语的句子。
a．I bought a book that was written by Lu Xun . = I bought a book written by Lu Xun .
b．Tell the children who are playing basketball not to do that . = Tell the children playing basketball not to do that .
c．The house that stands at the corner was built in 1987 . = The house standing at the corner was built in 1987 .
d．We have nothing that we should fear . = We have nothing to fear .
e．The book that is on the table is expensive . = The book on the table is expensive .
○5 引导词when, where和why可用相应的表示时间（in, on, at, during等）、地点（in, on, at等）和原因（for）的介词＋which 表达为介宾结构。
a．I still remember the day when I met her for the first time . ---- I still remember the day on which I met her for the first time .
b．That is the place where I went when I was a child . ----- That is the place to which I went when I was a child .
c．May I know the reason why you are late ? ----- May I know the reason for which you are late ?
○6 在定语从句中，不能再出现指示先行词的指示代词。
I just can't find the book which/that she lent it to me .（×）---- I just can't find the book which/that she lent to me .（√）
○7 注意下面的变化：
a． This is the house(不作lived的宾语) where we lived last year .
This is the house(作lived in的宾语) which/that we lived in last year .
b． This is the day (不作left的宾语)when we left for Shenzhen .
This is the day (作spent的宾语)which/that we spent in Shenzhen .
○8 限制性定语从句和非限制性定语从句的区别：
a． 限制性定语从句：是句中不可缺少的组成部分，没有从句，先行词意思不明确，主句也不完整，从句主句不用逗号分开。
b． 非限制性定语从句：是主句先行词的补充说明，没有从句并不影响主句意思的明确或完整，这种定语从句一般用逗号和主句分开，在非限制性定语从句中，一般不用that。
◎ Last Sunday they reached Dalian, where a meeting was to be held .
◎ She has two brothers, who are both doctors .
Ⅲ There be 句型
1． 英语"There + be + (not)"结构表示"有（没有）某人或某物"时，there 是无词义的引导词，be是谓语动词，它后面的名词是主语，两者再数上必须一致。句末往往有表示地点或时间的状语。
2． 肯定句：There +(助动词或情态动词)＋be 主语＋地点（时间）状语。
There is a pen on the table . / There will be a football match tomorrow .
3． 否定句：There + be(助动词或情态动词)＋not（any）(或＋no)+ 主语…。
There are not fairies in the world . / There wasn't a underground in Shanghai before ./ There won't be a football match tomorrow .
4． 一般疑问句：Be + there +(any) +主语… ？ / 助动词或情态动词 ＋ there +be +(any) + 主语… ？
Is there anything I can do for you ? / Will there be cloud tomorrow ?
5． 特殊疑问句：疑问词（＋名词）＋be ＋there + 状语 ？
How many weeks are there in a year ? / What is there on the desk ? / Where will there be a football match tomorrow ?
6． 如果there +be 之后是并列主语，应根据离be 最近的名词来选择be的形式。
There is a apple and two pears on the table . / There are two pears and a apple on the table .
7． 含有引导词there 的句子用seem to be , happen to be , used to be 或live 等作谓语的结构。
There happened to be an old friend of mine in the shop . / There used to be a temple here