序数词的构成
①序数词多数由"基数词-th"构成，序数词前一般加定冠词the
②少数序数词构成属特殊情况
e.g. One-first two-second three-third five-fifth eight-eighth nine-ninth twelve-twelfth
③以y结尾的十位整数，先将y改为i，再加-eth e.g. thirty-thirtieth
④21以上的多位数，要将末位数改为序数词，前面其他位数仍用基数词
e.g. eighty-three-eighty-third nine hundred and sixty-two-nine hundred and sixty-second
⑤序数词的缩写形式由阿拉伯数字加序数词的后两个字母构成
e.g. first-1st second-2nd
