Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
TOR, ?, VQT, WRU, XSV
Answer & explanation
Correct answer: option 1

Explanation:
TOR, ?, VQT, WRU, XSV
The logic followed here is :
T → (+1) → U → (+1) → V → (+1) → W → (+1) → X
O → (+1) → P → (+1) → Q → (+1) → R → (+1) → S
R → (+1) → S → (+1) → T → (+1) → U → (+1) → V
So, the letter-cluster that replaces the (?) to complete the series is "UPS"