Rules for "a/an"

1. Use "a" only with single nouns

1.1. Ej:

1.1.1. A coach

1.1.1.1. My brother is a coach

1.1.2. A lion

1.1.2.1. In the zoo there a lion

1.1.3. A banana

1.1.3.1. Yesterday I ate a banana

2. Use "an" with words that stars avowel

2.1. Ej:

2.1.1. An airplane

2.1.1.1. An airplane crashed in the city

2.1.2. An egg

2.1.2.1. The hen laid an egg

2.1.3. An apple

2.1.3.1. My mom eats an apple