Which of the following letter cluster will replace the blank (___) in the given series?
PRQ, QSR, _____, SUT, TVU

Correct option is C

Given: PRQ, QSR, _____, SUT, TVU
Each letter in the cluster follows the +1 logic where each letter in the next term is incremented by 1 from the previous term.
First letters:
P, Q, R, S, T (clearly follows the +1 logic).
Second letters:
R, S, T, U, V (follows the +1 logic).
Third letters:
Q, R, S, T, U (follows the +1 logic).
So, the missing term is:
First letter: R (+1 from Q)
Second letter: T (+1 from S)
Third letter: S (+1 from R)
Thus, the missing letter cluster is RTS.
The correct option is (c) RTS.