基数词变序数词规律:1.基变序，有规律，词尾加上th(fourfourth,sixsixth)2.一,二,三,特殊记,词尾分别t,d,d。(onefirst,twosecond,threethird) 3.八去t,九去e,f来把ve替。(eighteighth, nineninth,fivefifth, twelvetwelfth)基数词变序数词规律:4.单词ty作结尾,ty变成tie。(twentytwentieth, thirtythirtieth)5.若是碰到几十几,只变个位就可以。(twenty-onetwenty-first twenty-six twenty-sixth)写出下列词的序数词形式。1.one_2.two_3.six_4.five_5.nine_6.twelve_7.eight_8.twenty-one_firstsecondsixthfifthninthtwelftheighthtwenty-first写出下列单词的基数词形式。1.third_2.fourth_3.tenth_4.twentieth_5.nineteenth_6.thirty-first_threefourtentwentynineteenthirty-one