Which of the following terms will replace the question mark (?) in the given series?
DBOI, FEQL, ?, JKUR, LNWU

Correct option is C

Given - DBOI, FEQL, ?, JKUR, LNWU
​1st letters:
D → F (+2), F → ? , ? → J (+2), J → L (+2)
So, the missing letter must be H (F +2 → H).
2nd letters:
B → E (+3), E → ? , ? → K (+3), K → N (+3)
So, the missing letter must be H (E +3 → H).
3rd letters:
O → Q (+2), Q → ? , ? → U (+2), U → W (+2)
So, the missing letter must be S (Q +2 → S).
4th letters:
I → L (+3), L → ? , ? → R (+3), R → U (+3)
So, the missing letter must be O (L +3 → O).
Find the Correct Option
The missing term is HHSO.
Answer:
(C) HHSO