Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
CJ, FM, ?, LS, OV

Given: CJ, FM, ?, LS, OV

Logic: Each letter shifts +3 forward in the alphabet.

First letters: (C,F,?,L,O)
C +3 → F
F +3 → I
I +3 → L
L +3 → O
Second letters: (J,M,?,S,V,)
J +3 → M
M +3 → P
P +3 → S
S +3 → V
Thus, the missing letter-cluster is IP.
Correct option is (a) IP