一、知识归纳基数词变序数词的规律：口诀：基变序，有规律。一、二、三、特殊记，词尾字母t,d,d. (如：first, second, third)。 八减t,九去e,（如：eighth, ninth）, f 来把ve替。（如：twelfth）. 单词ty作结尾，ty变成tie(如：twentieth).若是碰到几十几，只变个位就可以。（如：twenty-first）1-100的序数词：1st-first；2nd-second；3rd-third；4th-fourth；5th-fifth；6th-sixth；7th-seventh；8th-eighth；9th-ninth；10th-tenth；11th-eleventh； 12th-twelfth；20th-twentieth；21st-twenty-first；22nd-twenty-second；29th-twenty-ninth；30th-thirtieth；31st-thirty-first；40th-fortieth；50th-fiftieth；60th-s
