first(第一）second（第二）third（第三）fourth（第四）fifth（第五）sixth（第六）seventh（第七）eighth（第八）ninth（第九）tenth（第十）eleventh（第十一）twelevth（第十二）thirteenth（第十三）fourteenth（第十四）fifteenth（十五）sixteenth（第十六）seventeenth（第十七）eighteenth（第十八）ninteenth（第十九）twentith（第二十）

　　1onefirst1st

　　2twosecond2nd

　　3threethird3rd

　　4fourfourth4th

　　5fivefifth5th

　　6sixsixth6th

　　7sevenseventh7th

　　8eighteighth8th

　　9nineninth9th

　　10tententh10th

　　11eleveneleventh11th

　　12twelvetwelfth12th

　　13thirteenthirteenth13th

　　14fourteenfourteenth14th

　　15fifteenfifteenth15th

　　16sixteensixteenth16th

　　17seventeenseventeenth17th

　　18eighteeneighteenth18yh

　　19nineteennineteenth19th

　　20twentytwentieth20th

　　1到20的序数词依次是firstsecondthirdfourthfifthsixthseventheighthninthtentheleventhtwelfththirteenthfourteenthfifteenthsixteenthseventeentheighteenthnineteenthtwentieth。