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

NAVIGATE, PCVIGATE, NAXKGATE, ? , NAVIGAVG

NAVIICTE

Explanation:

NAVIGATE, PCVIGATE, NAXKGATE, ? , NAVIGAVG

The logic followed here is :

N → (+2) → P → (-2) → N → (0) → N → (0) → N 

A → (+2) → C → (-2) → A → (0) → A → (0) → A

V → (0) →  V → (+2) →  X → (-2) → V → (0) → V 

I → (0) → I → (+2) → K → (-2) →  I → (0) → I 

G  → (0) → G → (0) →  G  → (+2) → I  → (-2) →  G  

A → (0) → A → (0) → A → (+2) → C → (-2) → A 

T → (0) →  T → (0) → T → (0) → T → (+2) → V  

E → (0) →  E → (0) → E → (0) → E → (+2) → G 

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