a)在不定代词，如：anything, nothing, everything, all, much, few, any, little等作先行词时，只用that，不用which。

All that is needed is a supply of oil.

b)先行词有the only, the very, the just修饰时，只用that。

He is the very man that helped the girl out of the water.

c)先行词为序数词(the last)、数词、形容词最高级时，只用that。

The first English book that I read was "The Prince and the Pauper" by Mark Twin.

d)先行词既有人，又有物时。

He talked about the teachers and schools that he visited.

e)当主句是以who 或which 开始的特殊疑问句时，用that 以避免重复。

Who is the person that is standing at the gate.

f)关系代词在从句中做表语

He is not the man that he used to be.