Correct option is B
According to the question-
1) N is shorter than L, but taller than O.
O < N < L
2) M is taller than N But shorter than L.
O < N < M < L
3) L is not as tall as k, the final arrangement is.
O < N < M < L < K
According to the height M is the middle person.
Hence, the correct answer is "M".