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

RAP, SCS, TEV, UGY, ?

VIB

Explanation:

RAP, SCS, TEV, UGY, ?

The logic followed here is :

R → (+1) → S → (+1) → T → (+1) → U → (+1) → V  

A → (+2) → C → (+2) → E → (+2) → G → (+2) → I  

P → (+3) → S → (+3) → V → (+3) → Y → (+53 → B  

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