in which /at which/where/which

就咁一個which 同 in which/ at which有咩分別

好簡單解釋，關係從句中的關係代名詞 which 是從句的主詞或受詞，例子如下：

The dog which attacked a child was taken away by officers from Agriculture, Fisheries and Conservation Department. (which 是 attacked 的主詞，指 the dog)

The book which I borrowed from the library is due today. (which 是 borrowed 的受詞，指 the book )

in which / from which / by which 等 which 並不是句中的主詞或受詞，而是 adverb phrase。

例句：
We are organizing a program in which students can practise their English. (正確)
We are organizing a program which students can practise their English. (錯)

students 是關係從句的主詞，their English 是受詞，which 指 a program。拆開做兩句

We are organizing a program. Students can practise their English in the program.

in which 在關係從句中是指 in the program.

有d人話 in which / at which = where。咁點解唔直接用where?

當 which 係指地方/地點時，in which / at which 才可用 where 代替。上面例子 which 指 a program，不是地方所以仍用 in which。

in which / at which 應該幾時用邊個?

要睇 adverb phrase 用 in 還是用 at

The coffee shop at which we met is in Shatin.
(We met at the coffee shop. 用 at)

The country in which he grew up has a small population.
(He grew up in a certain country. 用 in)

以上兩句都可用 where。

In Which

完整且正確關係副詞 觀念，看這裡。