A control group is the group that receives no changes in a experiment and is used as a benchmark. For example, a experiment where you wanted to know if plants can live without water, one of the treatments would be not giving them water. The control group would be the group that received water, like normal. Back to the question: Usually, music isn't played. Therefore no music would be the control group.
*Since you forgot to put the options, I can't be 100% sure, but I'm almost positive that this should be the answer.*
