Select the term that will complete the following letter series.

QN, RP, TS, WW, _____, FH

AB

Explanation:

QN, RP, TS, WW, _____, FH

The logic followed here is :

Q → (+1) → R → (+2) → T → (+3) → W → (+4) → A → (+5) → F

N → (+2) → P → (+3) → S → (+4) → W → (+5) → B → (+6) → H

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