关系代词that和which 都可以指物,that 和Who 都可以指人,其用法区别：
1）不用that的情况
a) 在引导非限定性定语从句时
(错) The tree,that is four hundred years old,is very famous here.
b) 介词后不能用
We depend on the land from which we get our food.
c)多用who 的情况
①关系代词在从句中做主语
A friend who helps you in time of need is a real friend .
②先行词为those ,people 时
Those who were either fools or unfit for their offices could not see the cloth .
③先行词为all,anyone ,ones ,one 指人时
One who doesn’t work hard will never succeed in his work .
④在There be句型中
There is a stranger who wants to see you .
⑤在被分隔的定语从句中
A new teacher will come tomorrow who will teach you German .
⑥在有两个定语从句的句子中,其一用who,其二用that,但若先行词后接两个以上的并列定语从句时,后一个必须重复前一个关系代词.
The student who was praised at the meeting is the monitor that is very modest and studies very hard .
There is a teacher who is always ready to help others and who enjoys what he does .
2) 只能用that作为定语从句的关系代词的情况
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.
Finally,the thief handed everything that he had stolen to the police.
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
