Ex, 2, p. 17.

1. Paul and Linda were singing while we were playing some music.

2.   What is that? — Bob is repairing his car at the moment.

3.   Sally is a nurse. She usually works at night.

4.   I was cleaning the windows when the telephone rang.

5.   Mike was reading a book when his mother called him.

6.   Are you busy? — No, what do you want me to do?