When I saw you, I was going to school.
I was doing my homework when my mother came.
When the postman came, we were leaving the house.
When the storm began, I saw driving home from work, I saw terriable traffic accident.
While we were walking to the station, the accident happened.
While I saw listening to the radio. I saw cooking dinner.
The lights went off while I saw doing my homework.
While you were playing the piano, I wrote a letter.