Answer & Explanation:
The sentence that includes a restrictive clause is sentence A: "Juliana's chili, which had gone through many recipe revisions, won first place at the chili cookoff."
A restrictive clause, also known as a defining clause, is a type of dependent clause that provides essential information about the noun it modifies. In this sentence, the restrictive clause "which had gone through many recipe revisions" provides essential information about Juliana's chili, specifically that it had been revised many times. This information is necessary to understand the sentence, so the clause cannot be removed without changing the meaning of the sentence.
The other sentences do not include restrictive clauses. Sentence B does not include any clauses at all, and sentences C and D include non-restrictive clauses, which provide non-essential information about the nouns they modify. Non-restrictive clauses are always set off by commas, but restrictive clauses are not.