Question

定语从句中只能用what，不能用that的几种情况？

Answer 1

定语从句中只能用which，不能用that的几种情况：
1、 在介词后面的关系代词用which而不能用that。即“介词+which（代物）” 。
例句：
The building in which Han Mei studied was very old.
韩梅在里边学习的那幢大楼很旧。
2、 在非限定性定语从句中用which，不能用that。
例句：
Crusoe's dog, which was very old now, became ill and died.
克鲁索的狗，现在已经很老了，病死了。

3、有两个定语从句，其中一个关系代词已有which，另一个宜用that。相反，如果其中一个为that，另一个宜用which。
例句：
Let me show you the novel that I borrowed from the library which was newly open to us.
让我给你看看我从新开放的图书馆借来的小说。
4、描述句中一般用which。
例句：
Beijing，which was China's capital for more than 800years.
北京是中国800多年来的首都。
5、those +复数名词之后，多用which 。
例句：
Shopkeeper want to keep a number of those goods which sell best.
店主想保留一些卖得最好的商品。

Answer 2

定语从句中的what等于all that，例如：All that I need is a good rest. =What I need is a good rest. 我所需要的就是好好体息。 这句话中的what不能改成that。