1first 2second 3third 4fourth 5fifth 6sixth 7seventh 8eighth 9ninth 10tenth 11eleventh 12twelfth 13thirteenth 14fourteenth 15fifteenth 16sixteenth 17seventeenth 18eighteenth 19nineteenth 20twentieth 21twenty-first 22twenty-second 23twenty-third.
一般情况下直接在基数词尾加th
123为特殊情况
整十要变y为ie再加th
词组（如21 22 23）只变后面一个单词
以t结尾直接加h
以ve结尾 变ve为f再加th