What is a sentence?

A Sentence is the expression of a thought in words.

Which of the following expressions contain words that have no connection, which contain words merely associated, and which are sentences?

1. Flowers bloom.

2. Ice melts.

3. Bloom ice.

4. Grass grows.

5. Brooks babble.

6. Babbling brooks.

7. Grass soar.

8. Doors open.

9. Open doors.

10. Cows graze.

11. Curling smoke.

12. Sugar graze.

13. Dew sparkles.

14. Hissing serpents.

15. Smoke curls.

16. Serpents hiss.

17. Smoke curling.

18. Serpents sparkles.

19. Melting babble.

20. Eagles soar.

21. Birds chirping.

22. Birds are chirping.

23. Birds chirp.

24. Gentle cows.

25. Eagles are soaring.

26. Bees ice.

27. Working bees.

28. Bees work.

29. Crawling serpents.

30. Landscape piano.

31. Serpents crawl.

32. Eagles clock.

33. Serpents crawling.