1. While we were on holiday, we were spending most of our time sightseeing.⇒ spent
2. Paul listened to his iPod, so he didn't hear the doorbell ring.⇒was listening
3.He is a most intelligent student in our class.⇒ the
4.Your new car is more cheaper than John's.⇒ bỏ từ "more"
5. He left college when he is 17⇒was