Complete the story,,once upon a time''

Ilive in a very nice and green city in the south of russia. our city is rather large. there are a lot of places of interest to visit there. museums, galleries, different monuments, parks and what not.  most of all i like to go to the central square. it's a place where all who love different kinds of sport meet. every evening you can see a lot of people roller-skating, riding bikes or making different tricks there. i meet with my friends there  and we have a really very good time together.

1. what (were you doing) when i (came) in? 2. when i (came) to his house, they (told) me that he (had left) an hour before. 3. on checking up his answers he (found) out that he (had made) several mistakes. 4. when i (left) home, the snow (had already stopped), but a strong wind (was blowing). 5. (have you read) this book? — yes, i (have read) it. i (think) it (is) very interesting. 6. what (are the children doing) now? — oh, they (are playing) the new table game which i (bought) for them the day before yesterday. 7. they (have reached) the corner of the street by now and (are standing) at the bus stop. 8. after we (had been walking) about two hours, we arrived at a picturesque glade covered with fresh grass. 9. we could not go out because it (had been raining) hard since early morning. 10. she (has been teaching) at our school for twenty years now. 11. ring me up as soon as you (come) home. 12. he (began) to write his composition at three o'clock. it is already eleven, and he (is still writing) it. he says he (will have finished) it by twelve. 13. we (have been helping) our librarian to put the books in the right order for already three days, but we (have arranged) only half the books.