Answer:
The words in the sentence that make up the appositive phrase are "beautiful antigue instruments" and the word that it renames is "guitars" (D).
Explanation:
An appositive phrase is a noun or noun phrase that renames another noun right beside it. Nonessential appositive phrases are always separated from the rest of the sentence with commas because the information they provide is not considered necessary to complete the meaning of the sentence. If dropped, the meaning of the sentence would be left unchanged (see 1).
1) My friend's brothers showed me their guitars.