Select the letter-cluster that can replace the question mark (?) in the following series.

CNQ, DOR, EPS, FQT, ?

​CNQ, DOR, EPS, FQT, ?

Logic: Each letter in the cluster is increased by 1 in alphabetical order.

C+1 → D+1 → E+1 → F+1 → G

N + 1 → O, O + 1 → P, P + 1 → Q, Q + 1 → R

Q + 1 → R, R + 1 → S, S + 1 → T, T + 1 → U

So, the next term in the series is GRU.​​​

Thus, the correct option is: (b)