Washington, D.C, is the capital of the United States of America.

A Proper noun is the name of a perticular person, place, or thing,

A Proper noun begins with a capital letter.

Can you summarize what you’ve understood in the above steps?

Choice A is incorrect. The words "is", "of", and "the" are not proper nouns. They are small words called "articles" or "helping verbs". Proper nouns are names of specific people, places, or things, like "John", "New York", or "Mount Everest".

Is, of, the

Choice B is incorrect because "is", "the", and "capital" are not proper nouns. Proper nouns are specific names of people, places, or things, like "New York City" or "John Smith".

Capital, is, the

Choice C is correct because "Washington, D.C." and "United States of America" are specific names (proper nouns) of a city and a country. Just like names for people, they start with capital letters.

Washington, D.C, United States of America

Choice D is incorrect because "America" and "capital" are not proper nouns. "America" is a proper noun because it’s the name of a specific country, but "capital" is a common noun because it refers to a general concept, not a specific place or thing.

America, capital

Nouns in this sentence - Washington, D.C, United States of America

Proper nouns in the given sentence - Washington, D.C, United States of America

Choice C

Can you summarize what you’ve understood in the above steps?