A dependent clause is a clause that cannot stand on its own. This means that it does not have a subject that matches a verb to form a complete sentence or thought. The correct answer for this case, would be A.
In the clause, “during intermission, while we were discussing the performance” there are prepositional phrases that need to be accompanied by an independent clause to make a complete sentence. A way to potentially complete this sentence would be “ during intermission, when we were discussing the performance, we ordered a popcorn from the concession stand in the theater.”
