The correct answer is C. can be removed from the sentence without hurting the meaning.
A parenthetical statement is often found either in parentheses or is separated from the rest of the sentence by commas. This is added information, which is not crucial to the meaning of the entire sentence. If it gets omitted, nothing is really changed.
For example: My friend, who is very beautiful, is standing there.
The phrase who is very beautiful is a parenthetical statement.