Which of the following letter-number clusters will replace the question mark (?) in the given series to make it logically complete?
GKO 11, IMQ 13, KOS 15, MQU 17, ?​

GKO 11, IMQ 13, KOS 15, MQU 17, ?​

Logic: Each letter + 2 , Number + 2

First letter  G + 2 → I, I + 2 → K, K + 2 → M, M + 2 → O 

Second letter K + 2 → M, M + 2 → O, O + 2 → Q, Q + 2 → S 

Third letter O + 2 → Q, Q + 2 → S, S + 2 → U, U + 2 → W 

Number 11 + 2 = 13, 13 + 2 = 15, 15 + 2 = 17, 17 + 2 = 19 

So, OSW 19 is the next term.

Thus, correct option is (a).