A series is given with one term missing. Select the correct alternative from the given ones that will complete the series.

ABCD, CUKA, ENSX, GGAU, ?

IZIR

Explanation:

ABCD, CUKA, ENSX, GGAU, ?

The logic followed here is :

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

B → (-7) → U → (-7) → N → (-7) → G → (-7) → Z

C → (+8) → K → (+8) → S → (+8) → A → (+8) → I

D → (-3) → A → (-3) → X → (-3) → U → (-3) → R

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