Article in English "THE" "A" and "AN"


I’m reaching out because my son is going through an exercise on articles in their English homework, learning how to correctly use "a," "an," and "the," but it seems a bit confusing sometimes. Could you help us make sense of it?
Here are a few sentences from the assignment:
1. ___ dog barked loudly last night.
2. He went to ___ store to buy some milk.
3. She adopted ___ dog from the shelter.
4. I heard ___ interesting story yesterday.
I’m not entirely sure when to use "the" versus "a" or "an," so any advice would be really helpful.

Greetings to you, Fedor Linkovich!
Let me help you understand the different uses of these three articles.
Firstly, use "the" to refer to a specific or particular noun or if the speaker and listener know the identity of the noun. 'The' can be used with singular or plural nouns.
'The' is also used if the noun has been mentioned in the previous sentences.
For example:
- The bananas on the table are ripe already.
- Rome is the capital of Italy.
- I have an uncle who works in the government, and he is the only relative I can rely on.
On the other hand, use "a/an" to refer to a non-specific or non-particular noun or when the identity of the noun is not known to the speaker or the listener. 'A/An' can only be used with singular nouns; thus, 'a/an' can also conote being a single count of something.
'A' is used before a noun that starts with a consonant letter, while 'an' is used before a noun that starts with a vowel letter or if the noun starts with a vowel sound.
For example:
- I will be eating a banana for dessert. (one banana)
- I always read a book before I go to bed. (any book)
- It had been an hour since I arrived at the cafe. (hour is pronounced with a silent /h/)