1. Their parents have been/have being friends since their childhood. 2. They have known/have been knowing him for many years. 3. I haven't seen/ haven't been seeng Tom since Monday. 4. We haven't been having/ haven't had a holiday for 5 years. 5. She hasn't been having/hasn't had dinner since morning. 6. I have understood/have been understanding text. 7. Mike has forgotten/has been forgotting to learn the poem. 8. Dave has been/ has been being a student for 2 years.