3124. I am not 100% sure on this, so i apologize if i am not right
Answer:
Musicals include every person's voice and their voices are incorporated in to one song that is trying to tell some form of a story. It wouldn't be a musical if there were one person right? So the "collaborative" part induces the fact that it is a musical with multiple roles for singing and acting. I hope this will help you, this answer came truly from me. Thank you.
