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

aYd, fTi, kOn, pJs, ?

uEx

Explanation:

Explanation:

aYd, fTi, kOn, pJs, ?

The logic followed here is :

a → (+5) → f → (+5) → k → (+5) → p → (+5) → u

Y → (-5) → T → (-5) → O → (-5) → J → (-5) → E 

d → (+5) → i → (+5) → n → (+5) → s → (+5) → x

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