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

MRT, TYA, AFH, HMO, ?

OTV

Explanation:

MRT, TYA, AFH, HMO, ?

The logic followed here is :

M → (+7) → T → (+7) → A → (+7) → H → (+7) → O  

R → (+7) → Y → (+7) → F → (+7) → M → (+7) → I 

T → (+7) → A → (+7) → H → (+7) → O → (+7) → V  

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