(1) I still remember the days which / that we spent together.
(2) I still remember the days when we worked together.
that 在限制性定语从句中既可指人又可指事或物。在下列情况下，只能用that 来引导定语从句：
1. 先行词是all , much, few, little, everything, anything, nothing 等不定代词时。例如：
Is there anything that you want to buy?
2. 先行词被all, few, little, much, every, some, no等词修饰或被the only, the very, the same, the last 等限定词修饰时。例如：
These are all the pictures that I have seen.
This is the very dictionary that is of great help.
My father and his teacher talked a lot about the things and the persons that they could remember.
Our school is not the one that it used to be.
This is the best English film that I have ever seen.
The first English novel that I read was A Tale of Two Cities.
6. 主句是who 或which 引导的特殊问句时。例如：
Who is the girl that is standing under the tree?
Which is the machine that we used last Sunday?
That's the reason for which he was late for school.
This is the book on which I spent 8 yuan.
This is the key which you are looking for.
This is the baby whom you will look after.
四、弄清as 和which 引导的非限制性定语从句指代整体时的区别
1. 位置上的区别：as 引导的非限制性定语从句的位置比较灵活，可以放在主句前，也可以放在主句后，还可插在主句的中间；而which 引导的非限制性定语从句只能放在主句之后。例如：
As is known to us all, the earth turns around the sun.
The earth, as is known to us all, turns around the sun.
The earth turns around the sun, as is known to us all.
The earth turns around the sun, which our parents once told us when we were very young.
2. 词义与联系上的区别：as 引导的非限制性定语从句与主句之间有着较为密切的上下文联系，as 本身含有“正如”之意；而which 引导的非限制性定语从句与主句之间在逻辑意义上近似并列句，which 本身表示“这”或“这一点”之意。例如：
Light travels faster than sound, as we all know.
Jack came late for school, which made his teacher angry.
Tom is one of the boys who are from the USA.
Tom is the only one of the boys who is from the USA.
(1)Is this factory _______ we visited last week?
(2)Is this the factory _______ we visited last week?
A. which B. where C. what D. the one
错句：Is this the train that they took it last Sunday?
分析：该题中that 已经代替先行词the train 在定语从句中充当及物动词took 的宾语，故重叠出现的宾语it必须删去。