Используйте либо Past Continuous либо Past Perfect Continues.
1. We were late. When we arrived, the teacher (?) for us. He was rather angry with us because he (?) for a very long time.
2. When the fire broke out they (?) TV. They didn’t notice is at once because they (?) a very interesting film.
3. We (?) for an hour when he turned up. We (?) when there was a terrible storm.
4. They (?) their dinner when we arrived. They (?) for half an hour.
was waiting. had been waiting. were watching. were watching.