21. Things have changed…………………………………. she's become headmaster. 22. The police have been looking for him…………………………………. a month. 23. Our dog has been ill…………………………………. two days. 24. I've been looking for this book…………………………………. a long time. 25. I've been working…………………………………. I got up. 26. The kettle has been boiling…………………………………. ten minutes 27. They have been living in Madrid …………………………………. 1972. 28. He has been in prison…………………………………. four years. 29. He has known about the fact …………………………………. a long time. 30. Conditions have changed a lot …………………………………. we were children. 31. Our teacher has been very ill …………………………………. the last month. 32. I haven't eaten anything …………………………………. twenty-four hours. 33. In fact he is always very rude. We have been waiting for him …………………………………. half an hour. 34. I haven't seen him for three years. It is because I haven't been there…………………………………. I left school. 35. I have been trying to mend this old fashioned car…………………………………. hours.