数字 -- 基数词---序数词---序数词简写
1 one first 1st
2 two second 2nd
3 three third 3rd
4 four fourth 4th
5 five fifth 5th
6 six sixth 6th
7 seven seventh 7th
8 eight eighth 8th
9 nine ninth 9th
10 ten tenth 10th
11 eleven eleventh 11th
12 twelve twelfth 12th
13 thirteen thirteenth 13th
14 fourteen fourteenth 14th
15 fifteen fifteenth 15th
16 sixteen sixteenth 16th
17 seventeen seventeenth 17th
18 eighteen eighteenth 18yh
19 nineteen nineteenth 19th
20 twenty twentieth 20th
21 twenty-one twenty-first 21st
（20往下都是有规律的,规律是twenty+10以内序数词,30 40 50 ……都是这样）
30 thirty thirtieth 30th