Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
BEC, CID, FOG, KUL, ?
Answer & explanation
Correct answer: option 2

Explanation:
BEC, CID, FOG, KUL, ?
The logic followed here is :
B → (+1) → C → (+2) → F → (+5) → K → (+7) → R
E → (+4) → I → (+6) → O → (+6) → U → (+6) → A
C → (+1) → D → (+3) → G → (+5) → L → (+7) → S
So, the letter-cluster that replaces the (?) to complete the series is "RAS"