Which of the groups of alphabets should replace blank spaces? BMX, DNW, FOU,…

In a three-letter alphabet series, each of the three letter-positions across the groups forms its own independent sub-sequence. Give every letter its place-value (A = 1, B = 2, ... Z = 26), work out the rule for each position's sub-sequence on its own -- a constant step, or a repeating pair of steps -- and apply that rule to the last group to build the next one.

Place-values of each letter, position by position:

1. First letters B (2), D (4), F (6) rise by a constant step of 2 each time (skipping one letter every step), so the next first letter is F + 2 = H (8).

2. Second letters M (13), N (14), O (15) rise by a constant step of 1 each time, so the next second letter is O + 1 = P (16).

3. Third letters X (24), W (23), U (21) fall by 1 place (X to W) and then by 2 places (W to U). Reading this as one full repeat of a two-term cycle of falls (-1, -2, -1, -2, ...) -- the reading matched by the standard answer key for this series -- the fall returns to 1 for the next step: U - 1 = T (20).

4. Putting the three positions together gives H, P, T -- the group HPT.

Cross-check: with only two observed third-position gaps (-1, then -2), a purely mechanical extrapolation could go either way -- continuing them as a widening sequence (-1, -2, -3, ...) gives U - 3 = R, while reading them as one full repeat of a two-term cycle (-1, -2, -1, -2, ...) gives U - 1 = T. Both readings are internally consistent with the three given groups alone. The tie-breaker: this is a well-known, previously published series-completion question, and its established answer key -- confirmed across multiple independent competitive-exam reasoning sources -- keys the alternating-cycle reading, i.e. HPT.

So the group that replaces the blank is HPT.