Réponse :
1. I have known him for eight years.
2. He has travelled in Australia for six months.
3. It has been a long time since he acted in this movie.
4. Have they actually been here since Monday?
5. Can I leave this here for a few hours?
6. She has been married since two years.
7. It's been twenty years since she died.
8. I will love him for ever.
9. I have not seen them since the birth of their son.
J'espere t'avoir aidée (: