A music ensemble is: Select one: A group of music phrases with complete meaning. A group of movements of a larger music composition. A group of musicians that perform as a unit. A group of movements unified by cadences.

A group of musicians that perform as a unit.

Explanation:

I leaned this in music class and I've played ensembles with drums

i believe their role is to instruct certain sections on when they are to join and when they are to stop