Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
CX, FU, IR, (?)

Correct option is C

Series: CX, FU, IR, (?)
First Letters: C → F → I
The sequence here seems to be moving forward by 3 in the alphabet each time:
C (3) + 3 = F (6)
F (6) + 3 = I (9)
Following this pattern, the next letter should be I + 3 = L.
Second Letters: X → U → R
This sequence is moving backward by 3 in the alphabet each time:
X (24) - 3 = U (21)
U (21) - 3 = R (18)
Following this pattern, the next letter should be R - 3 = O.
Conclusion: The next term in the series is LO.
Correct answer: (c) LO