Select the letter-cluster that can replace the question mark (?) in the following series.
DAG, FCI, ? , JGM, LIO
Answer & explanation
Correct answer: option 4

Explanation:
DAG, FCI, ? , JGM, LIO
The logic followed here is :
D → (+2) → F → (+2) → H → (+2) → J → (+2) → L
A → (+2) → C → (+2) → E → (+2) → G → (+2) → I
G → (+2) → I → (+2) → K → (+2) → M → (+2) → O
So, the letter-cluster that replaces the (?) to complete the series is "HEK"