(a) A, H, I, M, O, T, U, V, W, X, Y are the letters having a reflectional symmetry about a vertical mirror.
(b) B, C, D, E, H, I, K, O, X are the letters having a reflectional symmetry about a horizontal mirror
(c) H, I, O, X are the letters having a reflectional symmetry about both the vertical mirror and the horizontal mirror.