Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.

MA, NZ, OY, PX, ?

QW

Explanation:

MA, NZ, OY, PX, ?

The logic followed here is :

M → (+1) → N → (+1) → O → (+1) → P → (+1) → Q

A → (-1) → Z → (-1) → Y → (-1) → X → (-1) → W

So, the letter-cluster that replaces the (?) to complete the series is "QW"