Which of the following letter-clusters will replace the question mark (?) in the given series to make it logically complete?
HUD, LXE, PAF, TDG, ?

HUD, LXE, PAF, TDG, ?

Logic: 1st +4, 2nd + 3, 1st + 1

H + 4 → L, L + 4 → P, P + 4 → T, T + 4 → X
Second letters:

U + 3 → X, X + 3 → A, A + 3 → D, D + 3 → G
Third letters:

D + 1 → E, E + 1 → F, F + 1 → G, G + 1 → H
Therefore, the next letter-cluster is XGH.

Thus, correct option is (d).