The correct answer is B. a star at the center of our solar system
Step-by-step explanation:
In grammar, the word "appositive" refers to a word, multiple words or phrases that are non-essential in the sentence but mainly work as a synonym or describe a noun in a sentence. This means appositives provide information about another word and also, as they are non-essential they are enclosed by commas, parentheses or similar punctuation mark. According to this, in the sentence presented the phrase that is an appositive is "a star at the center of our solar system" because this section describes the noun and also subject "sun", besides as it is an appositive it is the section enclosed in parentheses.