1-20的序数词

one—first  two—second  three—third

four—fourth  five—fifth  six—sixth 

seven—seventh  eight—eighth 

nine—ninth  ten—tenth  

eleven—eleventh  twelve—twelfth 

thirteen—thirteenth 

fourteen—fourteenth  fifteen—fifteenth

sixteen—sixteenth  

seventeen—seventeenth

eighteen—eighteenth

nineteen—nineteenth

twenty—twentieth