英语序数词1-20是 :
first;second; third;fourth; fifth
sixth; seventh; eighth; ninth;tenth
eleventh;twelfth; thirteenth;fourteenth;fifteenth
sixteenth;seventeenth;eighteenth; nineteenth; twentieth
first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth, thirteenth, fourteenth, fifteenth, sixteenth, seventeenth,eighteenth, nineteenth, twentieth