Answer:
"Thomas Jefferson, the third president of the United States, was an important contributor to the Declaration of Independence."
Explanation:
Jefferson: The "J" in Thomas Jefferson should be capitalized because it is the name of a person. Names are proper nouns and should always be capitalized.
president: "President" should only be capitalized when it's at the beginning of the sentence (like it was in this case), when it's used right before a name (e.g. "President Joe Biden") or when you use it to refer directly to a specific person (e.g. "I need to talk to the President"). "President" in and of itself is just a title, like "editor" or "cashier", not a proper noun.
States: In this case, the "States" is part of the "United States", which is the name of a nation, meaning it's considered a proper noun and thus should be capitalized.
contributor: "Contributor" doesn't refer to any specific entity, so it's not a proper noun and therefore should not be capitalized.
Independence: Similar to the "United States", "Independence" is part of the name "Declaration of Independence", which is a proper noun and needs to be capitalized.
As a general rule of thumb, if you can say the word on its own and know specifically who or what is being referred to, it's a proper noun. For example, "writer" would not be a proper noun because it would be impossible to tell who "writer" is if it were alone, without any context. But "J.K. Rowling" would be a proper noun because that refers to one specific, identifiable writer.
