1 one first 2 two second 3 three third 4 four forth 5 five fifth 6 six sixth 7 seven seventh 8 eight eighth 9 nine ninth 10 ten tenth 11 eleven eleventh 12 twelve twelveth 13 thirteen 14 fourteen 15 fifteen 16 sixteen 17 seventeen 18 eighteen 19 ninteen 13~19的序数词都是基数词直接加th 20 twenty twentieth 往后，二十几就是twenty加上几，比如23就是twenty-three，序数词twenty-third，其基数词和序数词形式跟前面一样。 30 thirty thirtieth 40 fourty fourtieth 50 fifty fiftieth 60 sixty sixtieth 70 seventy seventieth 80 eighty eightieth 90 ninty nintieth 100 one hundred one hundreth
