定语从句用that的八种情况

a)当不定代词，如 anything, nothing, everything, all, much, few, any, little 等作先行词时，通常用 that，而不用 which。

All that is needed is a supply of oil.

b)若先行词有 the only, the very, the just 修饰，一般用 that。

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

c)如果先行词是序数词（the last）、数词、形容词最高级，通常用 that。

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

d)若先行词既有人又有物时，通常用 that。

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，为避免重复，用 that。

Who is the person that is standing at the gate.

f)关系代词在从句中作表语时，常用 that。

He is not the man that he used to be.