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

GIM GHJ FJR GKS

GKS

Explanation: ABD, CEI, EHN, ? The logic followed here is : A → (+2) → C → (+2) → E → (+2) → G  B → (+3) → E → (+3) → H → (+3) → K  D → (+5) → I → (+5) → N → (+5) → S    So, the letter-cluster that replaces the (?) to complete the series is "GKS"