on which 和 in which 都可以用來引導定語從句，修飾先行詞，區別在於介詞on/in 這取決於先行詞的搭配
比如:
I can"t forget the day on which we had a party.這個句子，先行詞是day，原本的搭配是on the day.
I like the room in which there are many toys.這句話的先行詞是room，片語搭配是in the room。
例句：
1.The school (that/which) he once studied in is very famous.
= The school in which he once studied is very famous.
2. I have a dresser in my bedroom, which there are many cosmetics on.
= I have a dresser in my bedroom on which there are many cosmetics.
固定搭配：
The plane may be several hours late, in which case there’s no point in our waiting. (固定搭配：in the case)
The little creature in which scientists are interested is known as ET.
(這裡"be interested in"是片語原因)
例題：
I can’t believe that the restaurant, ______ I have eaten such wonderful meal, is going to be close down. A. where B. at which C. about which
【解答】選B。這個是非限制性定語從句，at which在功能上等於where，但就本題而言只能選at which。因為at which I have eaten such wonderful meal是一個插入語，where固然可以引導，但是由於前面有了一個逗號，就只能用at which了。“我難以相信我曾經在裡面美美地吃過幾頓大餐的飯店就要關張了。”非限制性定語從句主要就是先行詞+逗號“，”+介詞+which或者是先行詞+逗號“，”+which，它和限定性定語從句的最顯著區別一個是有逗號，一個是非限制定語從句總有which。
in which:在......裡面；on which:在......的上面，或具體時間的某一天
on which 和 in which 都可以用來引導定語從句，修飾先行詞，區別在於介詞on/in 這取決於先行詞的搭配
比如:
I can"t forget the day on which we had a party.這個句子，先行詞是day，原本的搭配是on the day.
I like the room in which there are many toys.這句話的先行詞是room，片語搭配是in the room。
例句：
1.The school (that/which) he once studied in is very famous.
= The school in which he once studied is very famous.
2. I have a dresser in my bedroom, which there are many cosmetics on.
= I have a dresser in my bedroom on which there are many cosmetics.
固定搭配：
The plane may be several hours late, in which case there’s no point in our waiting. (固定搭配：in the case)
The little creature in which scientists are interested is known as ET.
(這裡"be interested in"是片語原因)
例題：
I can’t believe that the restaurant, ______ I have eaten such wonderful meal, is going to be close down. A. where B. at which C. about which
【解答】選B。這個是非限制性定語從句，at which在功能上等於where，但就本題而言只能選at which。因為at which I have eaten such wonderful meal是一個插入語，where固然可以引導，但是由於前面有了一個逗號，就只能用at which了。“我難以相信我曾經在裡面美美地吃過幾頓大餐的飯店就要關張了。”非限制性定語從句主要就是先行詞+逗號“，”+介詞+which或者是先行詞+逗號“，”+which，它和限定性定語從句的最顯著區別一個是有逗號，一個是非限制定語從句總有which。