Select the letter-cluster from among the given options that can replace the question mark (?) in the following series.
KABL, MCDN, OEFP, QGHR, ?

Given:
KABL, MCDN, OEFP, QGHR, ?
Solution:
The position of letters according to the English alphabet series:

First letters:

K (11th letter), M (13th letter), O (15th letter), Q (17th letter)

Pattern: +2 for each step.

Next: Q (17) + 2 = S

Second letters:

A (1st letter), C (3rd letter), E (5th letter), G (7th letter)

Pattern: +2 for each step.

Next: G (7) + 2 = I

Third letters:

B (2nd letter), D (4th letter), F (6th letter), H (8th letter)

Pattern: +2 for each step.

Next: H (8) + 2 = J

Fourth letters:

L (12th letter), N (14th letter), P (16th letter), R (18th letter)

Pattern: +2 for each step.

Next: R (18) + 2 = T

Step 2: Combine the letters

The next cluster is: SIJT

Final Answer: SIJT