简写是根据词尾判别的
first-st second-nd third-rd
因此
1 first 简写1st
2 second 2nd
3 third 3rd
4 fourth 4th
5 fifth 5th
6 7 8 9 10 都是th
11th eleventh 11th 一定要记住11不是11st,而是11th,因为是eleventh,不是ten-first
12 13也一样
所以11~20都是 ……th
从21开始就有规律了
21 twenty-first 所以是 21st
22 twenty-second 所以是 22nd
23 twenty-third 所以是 23rd
24 twenty-forth 所以是 24th
即个位是1就是st,个位是2就是nd,个位是3就是rd,其他个位就是th（务必记住20以后才适用,11,12,12是例外,都用th）
