ANSWER: E
PATTERN:
1. Multiple A's every after 2 letters are just extra, remove them all.
B, C, A, D, (?), A, H, I , A, K, O, A, X
B, C, D, (?), H, I, K, O, X
(Now you have a series of letters which are arranged from their position in the alphabet)
2. Check logical pattern, all of them are equivalent to their vertical mirror image. ?