2b
1. Is it snowing at the moment?
2. Does it snow in November?
3. It never snow in August.
4. It is snowing
5. Will it snow tomorrow?
6. Did it snow yesterday?
7. Does the sun shine every day?
8. The sun doesn't rise early in autumn
9. Sophia Paleologus came to Moscow...
10. refused
11. is sitting
12. pays
13. will be
14. are you thinking
15. do you think
16. skies
17. he is skiing
18. to ski
19. are skiing
20. skied
21. didn't ski
Насчет 13, 14, 15 и 19 не уверена.