Which of the following letter-clusters will replace the question mark (?) in the given series ?

DAJ, GEL, JIN, MMP, ?

PQR

Explanation:

DAJ, GEL, JIN, MMP, ?

The logic followed here is :

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

A → (+4) → E → (+4) → I → (+4) → M → (+4) → Q

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

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