一二三，全改变
八去t，九去e
字母f代ve
y变i，后面加e别忘记
几十几，前基后序莫乱记

one→first, two→second, three→third
five→fifth, twelve→twelfth
eight→eighth
nine→ninth
twenty→twentieth
thirty-three→thirty-third

容易混淆的基数词变化
four→fourteen→forty
five→fifteen→fifty
eight→eighteen→eighty
nine→nineteen→ninety