Relative Pronouns: Who, That, Which

Relative clauses add information about a noun in the main clause.  

Use the relative pronoun who or that for people. Use the relative pronoun that or which for things and animals.

The man was talking to the tourists. He was friendly.

The man who/that was talking to the tourists was friendly. (relative clause)

The computer company is making a good profit. It is called Easy Surf. The computer company that/which is making a good profit is called Easy Surf.

We can use the past progressive with while to talk about actions that were happening at the same time: 

Mohammed was working on the computer while his brother was talking on the phone.

While you were working at the photography studio, I was studying graphic design at college.

They were waiting for their father at the office while their father was waiting for them at home.

While she was talking with her sister downstairs, her mother was looking for her upstairs.