Prepositions and relative clauses

A relative pronoun can be the object of a preposition: 

I found the keys which I was looking for.

That´s the woman who(m) I´m in love with.

• In informal English we usually put the preposition at the end of the relative clause and we omit the relative pronoun: 

I found the keys I was looking for

That´s the woman I´m in love with.

• In formal English the preposition may come at the beginning of the relative clause, before the relative pronoun.

I found the keys for which I was looking.

That´s the woman with whom I´m in love.

Note: We cannot put a preposition before that or who

More examples:

• listen to

The music is good. Julie listens to the music.
→ The music (which / that) Julie listens to is good.

• work with

My brother met a woman. I used to work with the woman.
→ My brother met a woman (who / that) I used to work with.

• go to

The country is very hot. He went to the country.
→ The country (which / that) he went to is very hot.

• come from

I visited the city. John comes from the city.
→ I visited the city (that / which) John comes from.

• apply for

The job is well paid. She applied for the job.
→ The job (which / that) she applied for is well paid

Exercise