Respuesta:
1. When the teacher came into the room, two boys were playing football.
2. Peter turned on the TV, but nothing happened.
3. When Helen was walking to school, she saw the old man again.
4. While we were running in the park, Mary fell over.
5. At 7:00 Tony got out of bed and went into the bathroom.
6. While Kate was drinking some milk, she dropped the glass.
7. While I was listening to music, I heard the doorbell.
