Answer:
You use an a when the next word <u>doesn't </u>have a vowel at the beginning of a word.
You use an when the next word <u>does</u> have a vowel at the beginning of a word.
Explanation:
It's all about grammar and how words go together or don't go together in different ways.
Dennis' hands were muddy. He washed them. (does that work?)
I say A but i need more context this is too vague
