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

FIY, HLD, JOI, LRN, NUS, ?

PXX

Explanation:

FIY, HLD, JOI, LRN, NUS, ?

The logic followed here is :

F → (+2) → H → (+2) → J → (+2) → L → (+2) → N → (+2) → P

I → (+3) → L → (+3) → O → (+3) → R → (+3) → U → (+3) → X

Y → (+5) → D → (+5) → I → (+5) → N → (+5) → S → (+5) → X

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