英语中的序数词的缩写形式的th是写在数字的后面还是写在数字的右上角?

都可以.如果用电脑打字,"th" 会自动跳上数字的右上角.
如果使用打字机,你会看到这:
(1) Mary celebrated her 11th birthday yesterday.
(2) October 24 is the 297th day of the year (298th in leap years) in the Gregorian calendar.There are 68 days remaining until the end of the year.
(3) 21st ; 22nd ; 23rd ; 3rd floor ;