Complete the sentences with the correct relative pronouns: who, which, that. ​

1) The children played in the snow that had fallen during the night.
2) This is the painting that I saw last week.
3) Can I talk to the man who put his car there?
4) This is the girl who sang that song.
5) The magazines that I'd ordered are at the post.
6) Our school, which we study in, was built in 1989.