preposition

[Apple]

Dear Teacher,

Sometimes , I see a preposition before the word " which/that/who" . Could someone teach me how to use this structure in a sentence ?

Tks !
B.rgds,
Apple

[Mister Micawber]

I think you see it only before 'which', Apple.

This is the book of which I am so fond.
The house in which I live is clapboard.
Opening bottles is not the job for which this was designed.


This is the book of which I am so fond. (formal)
This is the book which I am so fond of. (informal)
I am fond of this book.

The house in which I live is ramshackle. (formal)
The house which I live in is ramshackle. (informal)
I live in this house.


Opening bottles is not the job for which this was designed. (formal)
Opening bottles is not the job which this was designed for. (informal)
This was not designed for opening bottles.