Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
ZC, XF, VI, TL, ?
Answer & explanation
Correct answer: option 1

Explanation:
ZC, XF, VI, TL, ?
The logic followed here is :
Z → (-2) → X → (-2) → V → (-2) → T → (-2) → R
C → (+3) → F → (+3) → I → (+3) → L → (+3) → O
So, the letter-cluster that replaces the (?) to complete the series is "RO"