they / walk to school / see / a movie star
they were walking to school when they saw a movie star
Grandpa/ sleep / visitors / arrived
Grandpa was sleeping when the visitors arrived
Jack / look out the window / the teacher / ask a question
Jack was looking out the window when the teacher asked a question
he/ have breakfast / phone / ring
He was having breafast when the phone rang/ When the phone rang, he was having breakfast