that和which做比较,主要在于它们在定语从句中的用法
that 和which在定语从句中都是做关系代词,指代先行词是事物的名词或代词（that还可以指代人,which 不可以）.通常情况下二者可以互换.
区别：
关系代词用that（不用which）的情况：
1.先行词是all,anything,everything,nothing等,关系代词应用that
That's all that he told me.
2.先行词前有the only,the same,the very 或no,little,much,any,every,all 等修饰时,关系代词应用that
She is the only person that I know in this company.
3.先行词前有序数词或形容词最高级修饰时,关系代词常用that
The first thing that I want to do is to take it away.
4.当先行词同时含有"人"或"物"时,关系代词应用that
5.在固定结构the same...that...; so...that...; such...that...以及it is/was...that...的强调句型中,要用that
This is the same park that we once visited.
6.如主句以there be开头时,关系代词应用that
There is a room that has two windows.
关系代词用which（不用that）的情况：
1.非限制性定语从句中关系代词一般要用which
She won the competition,which made the whole family very happy.
2.关系代词前如有介词,关系代词须用 which; 如把介词移至句末,可用that(或省略)
There’s only one problem about which they disagree.
This is the key (that) she was looking for.
3.如果先行词是that,关系代词应用 which
I know that which you told me.
4.如先行词和定语从句之间被其它较长的成分分隔,常用which
Larry told her the story of the young airman which I narrated at the beginning of this book.(先行词为story)
5.在"those+复数形式的名词"结构中,其后的关系代词多用which
A shop should keep a stock of those goods which sell best.
6.一个句子中如有两个定语从句,第一个定语从句用了关系代词that,第二个从句中的关系代词宜用which;但在平行结构中,应重复同一个关系代词
This is the book that you bought which you have lost.
I have a house which is located on the hillside,which faces the south.
此外,that还可引导同位语从句,which不能
I have heard the news that they had won the game.
