CHOOSE for or since TO COMPLETE THE SENTENCES
11. I've been looking for this book………. a long time.
12. I've been working………. I got up.
13. The kettle has been boiling………. ten minutes
14. They have been living in Madrid ………. 1972.
15. He has been in prison………. four years.
16. He has known about the fact ………. a long time.
17. Conditions have changed a lot ………. we were children.
18. Our teacher has been very ill ………. the last month.
19. I haven't eaten anything ………. twenty-four hours.
20. In fact he is always very rude. We have been waiting for him ………. half an hour.