Which pair of letters comes next in the series AZ, BY, CX, DW, ?

Explanation

1. 01

   First letters: A, B, C, D, moving forward one place, so the next is E.

2. 02

   Second letters: Z, Y, X, W, moving back one place, so the next is V.

3. 03

   Each pair is a letter with its opposite (the two positions add to 27). The next pair is EV.