(1)当先行词是人时，只用that

The people that lived here is a dentist.

(2)当先行词是两个或两个以上的人或物，用that

(3)当先行词是all,much,many,little,something,anything,eveything,nothing,none等词时，只用that

(4)先行词是系动词be后边的表语或关系代词本身是从句中的表语时，用that

This is a song that will be popular soon.

(5)主句用there be句型开头时，主语若指物，多用that

There is a position in the car that is still free.

(6)当先行词是最高级形容词或被最高级形容词修饰时用that

(7)当先行词被序数词修饰时

The third university that we visited is Beijing University.

(8)当先行词被very,only,one of,any,all,no,little,few等修饰时

(9)以who/which开头的句子中为避免重复，用that.

(1)在限定性定语从句中，作介词宾语提前时，只用which

This is the ship in which.......

(2)非限定性定语从句中，只指物。