Please help me with these ARTICLES
I was doing my exercise and bumped into the following sentences:
1. AN NBC news program is going to be changed following the advice of the reviewers.
2. They are developing A one-hour program that may interest older viewers.
How confused I am because I have always thought that AN is followed by a word starting with a vowel, but here in this case, it is followed by "NBC", which starts with an "N"
Similarly, a is followed by a word that begins with a consonant, but here in this case, it is followed by "one-hour".
Could you please explain these cases and copy a link that talks intensively about this phenomenon for me?