2. Articles: Acording to the oxford dictionaries it is a determiner that introduces a noun phrase a/an are considered infinite articles and they are used to introduce new concepts into a discourse.
3. Use "a", "an" Only with singular nouns.
4. Diferences: If the indefinite article"a" becomes "an" if the following noun begins with a vowel (a,e,i,o,u).
5. Articles a-an
6. Use "an" with words that star with a vowel sound
7. An + vowel (a,e,i,o,u) an apple, an El Salvador, an orange
8. a: A + Consonant. Examples: It is a bus, a book, a vehicle.
9. Remember the use of articles a or an: we use a or an before countable nouns in the singular
