What letters of the English alphabet have reflectional symmetry $(i.e.,\ symmetry\ related\ to\ mirror\ reflection)$ about.
$(a)$. a vertical mirror
$(b)$. a horizontal mirror
$(c)$. both horizontal and vertical mirrors

Reflective symmetry is a type of symmetry where one-half of the object reflects the other half of the object. It is also known as mirror symmetry. The line of symmetry can be in any direction, horizontal, vertical, slanting, etc. 

$(a)$. Vertical symmetry - A, H, I, M, O, T, U, V, W, X, Y

$(b)$. Horizontal symmetry - B, C, D, E, H, I, K, O, X

$(c)$. Both horizontal and vertical symmetry - O, X, I, H

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