Which pair of letters comes next in the series AZ, CX, FU, JQ, ?

Explanation

1. 01

   First letters: A = 1, C = 3, F = 6, J = 10. The jumps are 2, 3, 4, so the next jump is 5, giving 15, which is O.

2. 02

   Second letters: Z, X, U, Q are the opposites of A, C, F, J (each pair of positions adds to 27).

3. 03

   The opposite of O is $27 - 15 = 12$, which is L. The next pair is OL.