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

CXB, HUI, MRP, ROW, ?

WLD

Explanation:

CXB, HUI, MRP, ROW, ?

The logic followed here is :

C → (+5) → H → (+5) → M → (+5) → R → (+5) → W

X → (-3) → U → (-3) → R → (-3) → O → (-3) → L

B → (+7) → I → (+7) → P → (+7) → W → (+7) → D

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