Complete the series: AZ, BY, CX, DW, ?

Correct — A.
Rule: first letter +1, second letter −1.

First letters: A, B, C, D → next is E
Second letters: Z, Y, X, W → next is V

Check: every pair is a letter and its opposite (positions add to 27). E = 5 and V = 22, and 5 + 22 = 27.

The next term is EV, option (a).

Why the others are wrong

• (b)
  FU — FU moves each letter two places: F is D + 2 and U is W − 2. The series moves one place per term, so after DW comes EV.
• (c)
  GV — G is D + 3, while the first letters rise one place at a time (A, B, C, D). V is right, but the first letter must be E.
• (d)
  GU — GU jumps three places forward and two back (G = D + 3, U = W − 2). Both letters overshoot the one-place moves of the series.

A series of two-letter terms is two series side by side. Read the first letters as one run and the second letters as another, then extend each by its own step.

Here A, B, C, D climbs one place per term and Z, Y, X, W falls one place. The pairs are also opposite letters, A–Z, B–Y, C–X, D–W, so the next pair must be E and its opposite, V.

Key facts

• Opposite letters have positions that add to 27: A–Z, B–Y, C–X, D–W, E–V.
• E is the 5th letter and V the 22nd.
• A letter's opposite sits at 27 minus its position.

Common traps

• Moving two places instead of one, which gives FU.
• Checking only the second letter: GV ends correctly in V but opens with G, three places after D.

No directly related past PYQ was found.