This is the book which / that you asked for. 这是你要的那本书。
I saw something in the paper that / which would interest you. 我在报上看到了一些你会感兴趣的东西。
区别1：引导非限制性定语从句时，通常只用 which。如：
Jack drove too fast, which was reckless. 杰克开车开得太快，根本不考虑后果。
We took what he said literally, which may have been a mistake. 我将他所说的照字面意思来理解，但可能错了。
The church, which dated back to the 13th century, was destroyed in an earthquake two years ago. 那座教堂是13世纪建成的，两年前在一次地震中被毁了。
区别2：直接放在介词后作宾语时，通常只用 which。如：
The treasure, some of which has been recovered, has been sent to the British Museum. 这些宝藏已送往大英博物馆，其中有一些是失而复得的。
We did a fashion shoot on the beach in which the girls were modelling swimwear. 我们在海滩拍了一组穿泳装做模特的女孩的照片。
The pianist made a conquest of every audience for which she played. 这位钢琴家以她的演奏征服了每一位听众。
区别3：当先行词是下列不定代词或被 much, little, none, all, few, every(thing)，any(thing)，no(thing) 等修饰时，通常用 that。如：
He grasped at anything that might help him. 任何对他可能有帮助的东西他都想抓住。
There was little that the enemy could do but surrender. 敌人无法，只有投降了。
All [Everything] that can be done must be done. 凡能做的事都必须做。
A wise man thinks all that he says, and a fool says all that he thinks. 智者思其所言，愚者言其所思。
区别4：当先行词有the very, the only, the same 等修饰时，通常用 that。如：
Those are the very words that he used. 那是他的原话。英语语法
This is the only example that I know. 我知道的例子只有这一个。
区别5：当先行词有形容词最高级或序数词(包括last, next等)等修饰时，通常用 that。如：
This is the most interesting story that I've ever read. 这是我所读过的最有趣的故事。
The first thing that we should do is to work out a plan. 我们应该做的第一件事是订个计划。
区别6：当关系代词在定语从句中用作表语时，通常用 that。如：
China is not the country (that) it was. 中国已不是过去的中国了。
He is no longer the person that he was. 他已经不是以前的那个样子了。
Our income is now double the amount that it was ten years ago. 我们现在的收入是10年前的两倍。
区别7：当先行词是一个既指人又指物的并列词组时，通常用 that。如：
He was watching the children and parcels that filled the car. 他望着塞满车的孩子和包裹。
The passengers and the suitcases that were still waiting had to be transferred to another plane. 仍在等待的乘客和行李只得改乘另一架飞机。
They log everyone and everything that comes in and out of here. 进出这里的所有人和物他们都会记录。
区别8：当要避免与 which 重复时，通常用 that。如：
Which is the book that you need most? 哪本书是你最需要的？
