1) When the bell rang the children ran into the classroom and took their seats.
2) When I opened the door, the lesson had begun and the teacher was explaining something to the class.
3) Before we took the boy to the theatre he had never seen a play.
4) By the time we arrived the party had finished.
5) What were you doing when I called you? - I was cooking.
6) When I got to the playground my friend had already left.
7) We had a good long holiday after we had done all the work.