Which letter cluster will replace the question mark (?) to complete the given series?

ACFD, CFHG, ?, GLLM, IONP

EIJJ

Explanation:

ACFD, CFHG, ?, GLLM, IONP

The logic followed here is :

A → (+7) → C → (+7) → E → (+7) → G → (+7) → I

C → (-8) → F → (-8) → I → (-8) → L → (-8) → O

F → (+9) → H → (+9) → J → (+9) → L → (+9) → N

D → (-10) → G → (-10) → J → (-10) → M → (-10) → P

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