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

CYU, XTP, SOK, NJF, ?

Given: CYU, XTP, SOK, NJF, ?

Logic: Letters are decreasing by - 5 in alphabetical order.

C - 5 = X, Y - 5 = T, U - 5 =  P

X - 5 = S, T - 5 = O, P - 5 = K

S - 5 = N, O - 5 = J, K - 5 = F

Similarly,

N - 5 = I, J - 5 = E, F - 5 = A

The next code is IEA.

Thus, correct option is (b).