定义：表示数目多少或顺序多少的词叫数词，数词分为基数词和序数词。表示数目多少的数词叫基数词；表示顺序的数词叫序数词。
I基数词
1.基数词的构成
（1）1-20
one,two,three,four,five,six,seven,eight,nine,ten,eleven,twelve,thirteen,fourteen,fifteen, sixteen, seventeen, eighteen, nineteen, twenty
（2）21-99 先说“几十”，再说“几”，中间加连字符。
23→twenty-three,34→thirty-four,45→forty—five,56→fifty-six,67→sixty-seven,78→seventy-eight,89→eighty-nine,91→ninety-one
（3）101—999先说“几百”，再加and,再加末两位数或末位数；
586→five hundred and eighty-six,803→eight hundred and three
（4）l,000以上,先从右往左数，每三位数加一个“,”,第一个“,”前为thousand.第二个“,”前为
million,第三个“,”前为billion（美式）或thousand ,million（英式）,然后一节一节地表示。
1,001→one thousand and one
9,785→nine thousand, seven hundred and eighty-five
18,423→eighteen thousand, four hundred and twenty-three
6,260,309→six million two hundred and sixty thousand three hundred and nine
750,000,000,000→seven hundred and fifty, billion（美式） seven hundred and fifty thousand million（英式）