What should come in place of the question mark (?) in the given series based on the English alphabetical order?
RDL, TFO, VHR, XJU, ?

Given: RDL, TFO, VHR, XJU, ?

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

For, 1st letter 

R + 2 = T, T + 2 = V, V + 2 = X, X + 2 = Z

For, 2nd letter

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

For, 3rd letter

L + 3 = O, O + 3 = R, R + 3 = U, U + 3 = X

So, the missing term is ZLX.

Thus, correct option is (a).