Three of these four letter pairs are built alike and one is not. Choose the odd one out: AZ, BY, DV, CX.

In AZ, BY and CX the place numbers of the two letters add up to 27 — 1 + 26, 2 + 25 and 3 + 24 — so the second letter stands as far from the end as the first stands from the beginning. In DV the places are 4 and 22, which add to 26. The proper partner of D would have been W, standing 23rd, so the pair is out by a single place, and that is exactly what makes it easy to pass over.