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

DJQC, ELTG, FNWK, GPZO, ?

HRCS

Explanation:

DJQC, ELTG, FNWK, GPZO, ?

The logic followed here is :

D → (+1) → E → (+1) → F → (+1) → G → (+1) → H

J → (+2) → L → (+2) → N → (+2) → P → (+2) → R

Q → (+3) → T → (+3) → W → (+3) → Z → (+3) → C

C → (+4) → G → (+4) → K→ (+4) → O → (+4) → S

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