1)不用that的情况
a) 引导非限定性定语从句时。例如:
(错)The tree, that is four hundred years old, is very famous here.
b) 介词后不能用。例如:
We depend on the land from which we get our food. 我们依赖土地获得食物。
We depend on the land that/which we get our food from.
2) 只能用that作为定语从句的关系代词的情况
a)在there be 句型中,只用that,不用which.
b)在不定代词,如:anything, nothing, the one, all, much, few, any, little等作先行词时,只用that,不用which.
c)先行词有the only, the very修饰时,只用that.
d)先行词为序数词、数词、形容词最高级时,只用that.。
e)先行词既有人,又有物时。例如:
All that is needed is a supply of oil. 所需的只是供油问题。
Finally, the thief handed everything that he had stolen to the police. 那贼最终把偷的全部东西交给了警察。