"A (a) use the prefix noun, but An (Ann) use the prefix, nouns that begin with a vowel, e, i, o, or u," then the rule is kinda wrong, correct it is not preceded by a vowel, but vote with a, e, i, o, or u.
"A (i) take the lead, but An (Anne) use before nouns beginning with vowels a, e, i, o or u" is the wrong rule is not valid. Is not preceded by a vowel But pronounced with an a, e, i, o, or u.
"A () used in the name, but An (ANN) used before nouns that begin with a vowel,,, a e i o or u" is the rule wrong. Right. Not preceded by the pool but pronounced with outdoor a e I,,, or, O U