THE ARTICLE IS SOOOO BAAD
I passed a test and it says that here should be an AN
I'd like AN MP3 player for my birthday!
Why in the world is that??

Question

Answer

"M" is pronounced "em". Em pee three.  So you use "an" for spoken fluency, as you would with any word beginning with a vowel sound.

Answer

Yes, I agree.  You would use "an" because of the vowel sound of MP3.  We have many exceptions to rule you learned. Sorry, but I think almost all languages have some exceptions when it comes to grammar rules.