Complete the series: GH, JL, NQ, SW, YD, ?

Explanation

First letters: G, J, N, S, Y, F, with successive jumps of 3, 4, 5, 6, and 7 letters.
Second letters: H, L, Q, W, D, L, with successive jumps of 4, 5, 6, 7, and 8 letters.
Therefore, the missing pair is FL.