My teacher reviewed an exercise, and corrected something I didn't understand.
This is a piece of what I wrote:
It took some time until they could reach an agreement, but it finally...
It made sense to use
an since agreement starts with a vowel.
My teacher, however, gave me this feedback:
Article: You said "...reach an agreement..." You should say "...reach a agreement..." because indefinite article, "an" is used before a vowel sound, "a" otherwise, so I changed a word 'an' to 'a'. e.g., "It took some time until they could reach a agreement..."
So I'm confused. Why should I use
a rather than
an in this case?
Unfortunately this is an online course and a random teacher is designated to review, thus I can't talk back to my teacher and ask (which is unfortunate).