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

PNNA, RPPE, TRRI, VTTO, ?

XVVU

Explanation:

PNNA, RPPE, TRRI, VTTO, ?

The logic followed here is :

P → (+2) → R → (+2) → T → (+2) → V → (+2) → X

N → (+2) → P → (+2) → R → (+2) → T → (+2) → V 

N → (+2) → P → (+2) → R → (+2) → T → (+2) → V

A → (+2) → E → (+2) → I → (+2) → O → (+2) → U

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