Answer:
A. The hopeful actors agreed to meet in the dressing room before the audition.
Step-by-step explanation:
An adverbial phrase is a kind of prepositional phrase that functions as an adverb. Therefore, it answers the questions Where? When? How? or Why? and can modify a verb.
In this sentence, we have two adverbial phrases.
1. in the dressing room
2. before the audition
They both modify the verb 'to meet'. The first one is answering the question "Where?" The second one is answering the question "When?"