Since или for. Урок английского языка

1. You haven't smoked sincefor two months.

2. We've been friends with Fred sincefor decades.

3. I haven't slept sincefor 48 hours.

4. We've been together only sincefor a few days.

5. I've read two books sincefor the weekend.

6. You have been watching TV sincefor hours.

7. He hasn't played the piano sincefor he was a boy.

8. He worked at that company sincefor ten years before he retired.

9. New ideas have been put into practice sincefor he was elected our leader.

10. They've been teaching here sincefor quite a long time.