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

Given: YOD, WNF, UMH, SLJ, ?

Logic: 1st letter - 2, 2nd letter - 1 and 3rd letter + 2 place.

For, 1st letter

Y - 2 = W, W - 2 = U, U - 2 = S, S - 2 = Q

For, 2nd letter

O - 1 = N, N - 1 = M, M - 1 = L, L - 1 = K

For, 3rd letter

D + 2 = F, F + 2 = H, H + 2 = J, J + 2 = L

So, the missing term is QKL.

Thus, correct option is (a).