太简单了,如下：基数——序数——序数缩写
10：tententh10th
20:twenty twentieth 20th
30:thirty thirtieth 30th
40:forty fortieth 40th
50:fifty fiftieth 50th
60:sixty sixtieth 60th
70:seventy seventieth 70th
80:eighty eightieth 80th
90:ninety ninetieth 90th