1. The students have been reading the lesson for 5 minutes when the teacher came into the classroom and interrupt them.
2. He has been writing poesys for 2 years when I met him.
3.How long have Mr. Barton been working before he was fired?
4. He is the student who has been selected for the national competition.
5. The scientist , whose invention was dangerous, escaped alive and unharmed.
6. The test that you had yesterday was very difficult and that's why you got a bad mark.