Each pair has two independent letters; treat them as two separate series.
Series: AZ, BY, CX, DW, ?
First letters: A, B, C, D, … move forward by one → next is E.
Second letters: Z, Y, X, W, … move backward by one → next is V.
Combining, the next term is EV.
in two-letter (or mixed) series, split the position 1 letters from the position 2 letters and solve each as its own sequence.
Here one runs A→B→C→D→E and the other runs Z→Y→X→W→V (mirror image).
Exam Tip
notice the elegant structure — each pair sums to the same value (A+Z, B+Y … are 'complementary' letters 27 apart), a neat cross-check that the pair EV (5 + 22 = 27) is correct.