Answer:
April, August, December, February, January, July, June, March, May, November, October, September.
Explanation:
Go by each letter in the alphabet and see if there are any months that start with the letter. For ones with more 1 month for that letter, compare the 2nd letter. If there are any that have the same first two letters, compare the 3rd.
Hope this helps!
P.S. Next time, post this in English instead of Mathematics. :)