Correct option is C
The first group covers letter 1: A.
The second group covers letters 3rd and 4th: C and D.
The third group covers letters 7th, 8th, and 9th: G, H, I.
The missing group should logically cover letters 13th, 14th, 15th, and 16th: M, N, O, P. Therefore, MNOP is the correct group.
Correct answer is (c) MNOP.