What comes next in the sequence?

Question

st, nd, rd, th, __, __.
Sorry about typos in previous question.

th, th

These are the two-letter endings to "ordinal" numbers, starting with the "first". See http://www.janbrett.com/piggybacks/ordinal.htm

Thanks for your example, but I still don't get it. I've tried to associate the alphabet with numbers and there's no pattern....

It's a pattern of the ending of the ordinal numbers in the English language.. a trick question. It's more about logic than about math. You have to look at patterns outside the realm of math.
firST
secoND
thiRD
fourTH
fifTH
sixTH
etc.

Thank you, I've tought about your reply and it makes sense now. The two-letter endings are in sequence.
1st, 2nd, 3rd, 4th, 5th, & 6th.
Thank you again............