Singular and plural nouns

A singular noun refers to exactly one person, place, or thing, while a plural noun refers to two or more.
Most plurals simply add -s, so "book" becomes "books", but the key point is how many the word stands for.

Deciding singular vs plural tells you which matching words to use.
A singular noun pairs with its, "it", and a verb like "was"; a plural noun pairs with their, "they", and "were".
Matching the noun to these words correctly is what the question is really testing.

A common tricky case is a proper noun — the name of one specific place, company, or group.
Even though a city holds many people, its name is one name, so "Antwerp" is singular and takes "its".
The same is true for a single company or team: one name, singular.

So to choose, first pin down how many the noun names.
"The city doubled its population" is singular, but "The cities doubled their populations" is plural.
Once you know the count, the singular or plural partner word follows automatically.

Is "Antwerp" a singular or plural noun, and which word fits? "Antwerp more than doubled ______ population in the 1400s."
(A) its
(B) their
Antwerp is the name of one city, so it is a singular noun.
A singular noun takes the singular possessive, so (A), "its", is correct.

Which word fits? "The three museums extended ______ opening hours for the festival."
(A) its
(B) their
"Three museums" names more than one, so it is plural.
A plural noun takes the plural possessive, so (B), "their", is correct.

Which word fits? "The committee announced ______ decision after a long meeting."
(A) its
(B) their
"The committee" is the name of one group acting as a single unit, so it is singular.
A singular noun takes "its", so (A) is correct.