AE : C :: KO : ? Which letter completes the analogy?

The answering letter stands exactly midway between the two given letters. A is 1st and E is 5th, and the 3rd place, C, lies halfway. K is 11th and O is 15th, so the halfway place is the 13th, which is M. 'L' is 12th and 'N' is 14th, the two places flanking the middle, and 'P' is 16th — one beyond O, which is carrying on past the pair instead of settling between them.