5也例外的 five->fifth12也例外 twelve -> twelfth但总体上来说,规律是一样的,5、12稍加变形后加thone firsttwo secondthree thirdfour fourthfive fifthsix sixthseven seventheight eighthnine ninethten tentheleven eleventhtwelve twelfththirteen thirteenthfourteen fourteenthfifteen fifteenthsixteen sixteenthseventeen seventeentheighteen eighteenthnineteen nineteenthtwenty twentieth