序数词1到31如下：
1. first
2. second
3. third
4. fourth
5. fifth
6. sixth
7. seventh
8. eighth
9. ninth
10. tenth
11. eleventh
12. twelfth
13. thirteenth
14. fourteenth
15. fifteenth
16. sixteenth
17. seventeenth
18. eighteenth
19. nineteenth
20. twentieth
21. twenty-first
22. twenty-second
23. twenty-third
24. twenty-fourth
25. twenty-fifth
26. twenty-sixth
27. twenty-seventh
28. twenty-eighth
29. twenty-ninth
30. thirtieth
31. thirty-first