Each of the following questions is based on the following alphabet series.
$A, B, C, D, E, F, G, H, I, J, K, L, M$
$N, O, P, Q, R, S, T, U, V, W, X, Y, Z$
If the alphabet is written in the reverse order and every alternate letter starting with $Y$ is dropped,which letter will be exactly in the middle of the remaining letters of the alphabet?

• A
  $M$
• B
  $N$
• C
  $O$
• D
  $M$ or $O$