Answer is **B, D, F, I, L, P, "T"**.

The letters count between B & D and D & F is "1".

Similarly between F & I and I & L is "2".

From this, we get same letter count between 2 combinations of letters in the series like {B&D , D&F} and {F&I , I&L}.

So for the next two series letter count { L&P and P&? } must be "3".

So 3 letters next to P is **T**.