Select the term that can replace the question mark (?) in the following series.

FX, IW, LV, OU, RT, ?, XR

Given: FX, IW, LV, OU, RT, ?, XR

Logic: First letters are increasing by +3, and 2nd letters are decreasing by -1.

First letter: F +3→ I  → L +3 → O +3 → R +3 → U +3 → X (24)

Second letter: X -1→ W -1 → V -1 → U -1 → T -1 = S -1 → R

The next pair will be: US

Thus, the correct option is (b) US.