到30的序数词为：
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-first 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。
