The correct answer for the question that is being presented above is this one: "c. the music in the Stardust Ballroom." The speaker compare “The Empty Dance Shoes” energy to the music in the Stardust Ballroom. In the Stardust ballroom, the energy of the music is high.
A complete subject is the simple subject, or the main word or words in a subject, along with any of the modifiers that might describe the subject.
To identify the complete subject in a sentence, ask yourself who or what performs the action in the sentence. When determining the complete subject, remember to include both the simple subject plus all of the words that modify it.
It acts as a collection of "puzzle pieces" that will complete the larger picture.