Which words in the sentence are an appositive phrase?
a piano, an old upright, had been stored in the basement.
a. in the basement
b. a piano
c. had been stored
d. an old upright

In the sentence "A piano, an old upright, had been stored in the basement", the correct appositive phrase is "an old upright". So the correct option in regards to the given question is option "d". Appositive phrase is actually a noun phrase. It actually renames a noun that is right beside it. It can either be a long or short combination of words, depending on the sentence in which it is used. Actually an appositive is a noun. Appositives will always be accompanied with a comma or brackets or dashes. Appositives are often introduced separately to the sentence.

Chope you get it right gl