in which, on which, of which......到底文法上如何使用 ?

其實這個是頗簡單的，那些of/in/at/in/... 都是relative clause的主詞在原句之前的preposition; 英式英文都會把preposition的調位至relative clause pronoun之前。

Jane came to my office on Monday at 8pm.
Monday was the day on which Jane came to my office at 8pm.
8pm was the time at which Jane came to my office on Monday.
Monday was the day on which and 8pm was the time at which Jane came to my office.

We bought a dozen eggs. We cooked five of them. The five were bad.
We bought a dozen eggs, of which five that we cooked were bad.

John arrived at South Station.
South Station was the station at which John arrived.
(ok: South Station was the station where John arrived.)
(More US-style: South Station was the station that John arrived at.)

I gave the book to John.
John was the one to whom I gave the book.
(US-style: John was the one who I gave the book to.)

I starred at the beautiful model.
The beautiful model was the one at whom I starred.
(ok: The beautiful model was the one whom I starred at.)
(US-style: The beautiful model was the one who I starred at.)

記得，當你把preposition移前之後，preposition之後一定不可以接that。這時候，英或美式英文都要用個which字。Who（英式英文嚴格上不會在這時候用who，因為有了preposition就一定是用accusative形，亦即是whom)/whom, where, when, how 沒有改變。

算有心機

其實都不是太難理解。 讓我擧一個例子：

英文 1：There is a shelf. On that shelf, a clock is placed.
英文 2：There is a shelf, on which a clock is placed.
中文： 那兒有一個架， 在架上面放了一個時鐘。

on which 在這裡的用法是把 英文1 的兩句串起來。 “on which a clock is placed" 可以視爲 "on that shelf, a clock is placed"。 which 是指 shelf； 而 on which 是指 在架上。 在 英文1 裏， 由於在前面的一句已經提過了 shelf, 再提 shelf 就會變得 redundant。 所以我們可以用 on which 把兩句串起來， 減少 redundancy。