Final answer:
The sentence 'a' correctly uses an appositive phrase to give additional information about Rebecca, identifying her as a talented artist and directly relating to the subject of painting.
Step-by-step explanation:
The question asks which sentence correctly uses an appositive phrase. An appositive phrase is a noun or noun phrase that renames another noun right beside it. The purpose of these phrases is to clarify the identity of the noun. In looking at the given options, sentence 'a' Rebecca, a talented artist, was working on a new painting, includes an appositive phrase. 'A talented artist' is the phrase that renames and gives additional information about 'Rebecca.' This highlights the artistry and talent she possesses which is directly tied to the subject of painting.
Sentences 'b', 'c', and 'd' do not contain appositive phrases. Although they provide additional information about Rebecca and her work, the structure of these sentences does not place a noun or noun phrase immediately next to another noun to rename or re-identify it.