[MSL]

A, an (ABCDEFGHIJKLMNOPQRSTUVWXYZ)

A, an (ABCDEFGHIJKLMNOPQRSTUVWXYZ):

An A (an a)
A B (a b)
A C (a c)
A D (a d)
An E (an e)
An F (an f)
A G (a g)
An H (an h)
An I (an i)
A J (a j)
A K (a k)
An L (an l)
An M (an m)
An N (an n)
An O (an o)
A P (a p)
A Q (a q)
An R (an r)
An S (an s)
A T (a t)
A U (a u)
A V (a v)
A W (a w)
An X (an x)
A Z (a z).

! The rule for "a or an" is based on pronunciation, not actual spelling.