Answer:
C. usage rate.
Step-by-step explanation:
As in the question, it is mentioned that Massage Envy offers massage services based on a subscription basis with a view to targeting the consumers that they get more or multiple treatments per month
So Massage Envy target the market segment via usage rate as it depicts the average sales per day so that they get to know how much they earned the revenue by offering multiple treatments to clients
hence, the correct option is C. usage rate