This question is incomplete, here is the complete question:
Decide if the underlined part of each sentence is an absolute phrase, an appositive phrase, a restrictive clause, or a nonrestrictive clause.
A. The concert that i attended was held last august.
B. The audience moved as one, the crowd swaying to the music.
C. The concert, which had been rescheduled, was sold out.
D. The band, a hometown favorite, came back for several encores.
ANSWER:
A. The concert that i attended was held last august: Restrictive clause
Adjective clauses are group of words having a subject and a verb and whose function is to modify nouns; they can be either restrictive or nonrestrictive. The clause “that I attended” is an adjective one because it is modifying the noun “the concert” and it is also restrictive because it is providing essential information to the noun “the concert” (Without the clause the meaning of the sentence would be incomplete or vague).
B. The audience moved as one, the crowd swaying to the music : Absolute phrase
Absolute phrases are phrases that provide further detail to a sentence, without being essential to it, and that are separated by a comma, like the underlined phrase.
C. The concert, which had been rescheduled, was sold out : Nonrestrictive clause
This clause is an adjective nonrestrictive one because it is providing further, and not essential, detail about the noun “the concert,” which means that without it, the sentence would still make sense.
D. The band, a hometown favorite, came back for several encores : Appositive phrase
Appositive phrases are phrases (groups of words without a subject or a verb) that rename, identify or give further information of another noun placed right beside it, like “a hometown favorite” which renames the noun besides it “the band.”