Answer:
11. This was the dirtiest looking dog I have ever seen.
12. My friend haven't seen me for many years when I met him last week.
13. After John had washed his clothes, he began to study.
14. She came into the room when they was watching television.
15. As soon as we find another apartment, we'll move.
16. She was playing the piano when our guests had arrived last night.
17. My mother will come to stay with us next weekend.
18. Violets blooms in the spring.
19. We haven't been living in England for the last two years.
20. I have never forget what you have just told me.
21. They preparing the Christmas dinner today.
22. I didn’t know what time it was, so I turned on the radio.
23. She says that she lived in the country when she was a child.
24. When the teacher came in, the pupil were playing.
25. Mary does not eat meat. She is a vegetarian.
26. They will go home after they will have finished their work./They went home after the had finished their work
27. In my country, it often snows a lot in winter.