一到三十的序数词
1st = first
2nd = second
3rd=third
4th=fourth
5th=fifth
6th=sixth
7th=seventh
8th=eighth
9th=ninth
10th=tenth
11th=eleventh
12th=twelfth
13th=thirteenth
14th=fourteenth
15th=fifteenth
16th=sixteenth
17th=seventeenth
18th=eighteenth
19th=nineteenth
20th=twentieth
21st=twenty-firstu
22nd=twenty-second
23rd=twenty-third
24th=twenty-fourth
25th=twenty-fifth
26th=twenty-sixth
27th=twenty-seventh
28th=twenty-eighth
29th=twenty-ninth
30th=thirtieth
说明
1、许多序数词是由相应的基数词后加th构成的，如：four / fourth，six / sixth，ten / tenth，sixteen / sixteenth，但是nine变为序数词是ninth，而不是nineth。
2、twentieth, thirtieth, fortieth等表示整十的序数词，由相应的基数词将词尾y改为ie，再加th构成。
3、first, second, third通常可缩写为1st, 2nd, 3rd。凡是以th结尾的序数词可缩写为“基数词＋th”：4th, 5th, 9th, 11th, 60th, 128th等。
4、非整十的多位数，将个位数变成序数词即可：twenty-first(第21)，thirty-sixth(第36)，ninety-ninth(第99)，three hundred and sixty-fifth(第365)等。
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