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

ADG, CGK, EJO, ? , IPW

GMS

Explanation:

ADG, CGK, EJO, ? , IPW

The logic followed here is :

A → (+2) → C → (+2) → E → (+2) → G → (+2) → I

D → (+3) → G → (+3) → J → (+3) → M → (+3) → P

G → (+4) → K → (+54) → O → (+4) → S → (+4) → W

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