Select the letter-cluster that can replace the question mark (?) in the following series.
TXB, QWE, NVH, KUK, ?

Given that series TXB, QWE, NVH, KUK,?

we know that alphabet position  A=1, B=2, C=3,...... and so on 

then we represent given series in the form of alphabet position 

20 24 2, 17 23 5, 14 22 8 , 11 21 11 , ?

from the above series going on this pattern first decreases -3 to next, second decreases -1 and the last third is increased 3 positions of an alphabet.

then in the same pattern? = (11-3) (21-1) (11+ 3) 

? = 8 20 14 (H T N)

therefore? = HTN Ans