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

qDx, nHs, kLn, hPi, ?

eTd

Explanation:

qDx, nHs, kLn, hPi, ?

The logic followed here is :

q → (-3) → n → (-3) → k → (-3) → h → (-3) → e

D → (+4) → H → (+4) → L → (+4) → P → (+4) → T

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

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