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

HBS, GDP, FFM, ?, DJG

EHJ

Explanation:

HBS, GDP, FFM, ?, DJG

The logic followed here is :

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

B → (+2) → D → (+2) → F → (+2) → H → (+2) → J 

S → (-3) → P → (-3) → M → (-3) → J → (-3) → G

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