只有在先行词为人和物,人或物得时候才能用that修饰,在that作主语的时候不能省略,在作宾语的时候可以省略.
1）被修饰的先行词为不定代词,如all,much,everything,anything,nothing,none,the one,something等时,只能用that.如：
Is there anything that I can do for you?
2）先行词被only,very,just,last,one of,all,no,little,few,any等词修饰时,只能用that.如：
The only thing that I want to do is to have a rest.
3）先行词是序数词或被序数词修饰时,只用that.如：
He was the first person that passed the exam.
4）先行词是最高级或被最高级修饰时,只用that
This is the best way that can solve the problem.
5）先行词既有人也有物时,只用that.如：
The film star and her film that you have just talked about are really very famous.
6）被修饰词为数词时,只用that.如：
He brought two cats yesterday.Now I can see the two that are playing in the garden.
7）如果两个从句,其中一个关系代词用which引导,则另一个用that以避名重复.如：
He built up a factory which produced things that had never been seen before.
8）主句是there be结构,修饰其主语的定语从句用that.如：
There is a book on the desk that belongs to Frank.
