1. I still remember the days which/that we spent together.
2. I still remember the days when we worked together.
1. 先行词是all, much, few, little, everything, anything, nothing等不定代词是，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。如：These are all the pictures that I have seen. This is the very dictionary that is of 指人great help.
3. 先行词既 指人又指物时。如：My father and his teacher talked a lot about the things and the persons that they could remember
4. 关系代词在定语从句中作表语时。如：Our school is not the one that it used to be.
5. 先行词被形容词的最高级或序数词修饰时。如：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。如：Who is the girl that is standing under the true Which is the machine that we used last Sunday
介词的选择与住句中先行词的搭配密切相关。如：That‘s the reason for which he was late for school. This is the book on which I spent 8 yuan.
注意：定语从句中谓语动词是含有介词的动词短语时，介词应放在动词之后，不能拆开放在关系代词前。如：This is the key which you are looking for. This is the baby whom you will look after.
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 放在主句之后。“周所周知，地球围绕太阳转”。这句话可以有以下几种表达方式（1）As is known to us all, the earth turns around the sun. （2） The earth, as is known to us all, turns around the sun. （3） The earth turns around the sun, as is known to us all. （4） 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。如：Light travels faster than sound, as we all know. Jack came late for school, which made his teacher angry.
关系代词在定语从句中作主语时，从句的谓语必须与先行词保持人称和数的一致。如：Tom is 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
2. 在定语从句中，关系代词或关系副词已经代替先行词独立地或与相应的介词一起在定语从句中充当了一定的成分，因此在定语从句中就不能再出现于关系代（副）词重叠的成分。如：Is this the train that they took it last Sunday （错句）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。