Insert the appropriate article-
I’m just going to ____ post office behind my house. I won’t be long.
a- a
b- an
c- the
d- no article

Hint: Articles, ‘a, an, and the’ are used with nouns to form appropriate noun phrases. We use articles to identify whether the mentioned noun is specific or generalized.

Complete answer:
 As given in the hint, articles are determiners that help in describing a noun.
Let’s look at the two types of articles-
Indefinite articles- ‘A and an’ are known as indefinite articles. They are used with generalized nouns. We use ‘a’ with singular nouns that begin with a consonant sound, whereas ‘an’ is used with singular nouns that begin with a vowel sound. For Example- An orange, a book, an apple, a ball, etc.
Definite article- ‘The’ is a definite article. It is used with particular nouns and proper nouns. We use ‘the’ with both singular and plural nouns. Example- The Amazon river, the ground, etc.
In the given question- We can conclude that X said I’m going to the post office behind my house. I won’t be long.
Here, we have used the definite article ‘the’ because we are talking about a specific post office.
Now, let’s examine the given options-
Option a- ‘a’ is an incorrect option because it is an indefinite article that is used with general nouns.
Option b- ‘an’ is an incorrect option because it is an indefinite article that is used with general nouns starting with a vowel sound.
Option c- ‘the’ is the correct option because ‘post office’ is a specific noun. The correct answer is Option ‘c’.

Note:
Articles act as adjectives because they help in describing nouns. Keep in mind, we cannot use indefinite articles to modify plural nouns or specific nouns.