Why Is the Ability to Track Purchases by Song Mix

Why is the ability to track purchases by song mix so important for Ferrante's clients?

A) Ferrante sells cheaper custom mixes than standard soundtracks available from other vendors.
B) It allows the clients to shape the store brand with music.
C) It gives the clients information on their competitors' products and services.
D) It allows the clients to increase sales by playing the songs that stimulate purchases.
E) It requires the clients to play certain songs no more than a few times in a shift.