"in which"點樣用,點解?

.....個in字唔係 not important 架....

首先你要知個which字既用法,不過我唔會講得太detail, assume你都識...

which:
1. 問句既開頭用呀, 例如問'邊一個係....'
e.g.which is your car?

2. 用黎講對等關係,或者修飾前面既字 多數用在 comma (,)之後
e.g. His age, which I think is 90, is hardly noticeable.

這個用法有時會用 in which,不過要係講到house,organization之類,會配個in字既noun先會用到
e.g. the house in which i live
the international organization in which U.S. participates
這個用法有時會配不同既preposition:
e.g. the horse on which i ride
He has a gun with which to defend himself

3. 第3個meaning又係有時會見到 'in which'既, 個意思係: 這/ 這樣的話,通常係講一件事引至另一樣野,咁既時候 which前面又係可以配唔同既preposition
睇下一d字典既例子:
He changed his mind again, after which I refused ever to go out with him anymore.
He may come tonight, in which case I will ask him about the issue.

無論係用法2定用法3,好多時,用左合適既preposition係which前面會好d,不過你要清楚幾時會邊一個preposition,如果唔係,例如你寫左: the horse in which i ride 就係錯喇....唔係成日都用in which,有時係 on which, after which, of which, by which, 你要分清楚,小心用先唔會錯....

Ex. In which bag you will find the ball?
means which bag you will find the ball
the "in " was not really important