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

ZVG, XRI, VNK, TJM, RFO, ?

PBQ

Explanation:

ZVG, XRI, VNK, TJM, RFO, ?

The logic followed here is :

Z → (-2) → X → (-2) → V → (-2) → T → (-2) → R → (-2) → P

V → (-4) → R → (-4) → N → (-4) → J → (-4) → F  → (-4) → B

G → (+2) → I → (+2) → K → (+2) → M → (+2) → O → (+2) → Q

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