Final answer:
To define the relationship between Customer and Product Usage, you should create the Product Usage property in the Customer class.
Step-by-step explanation:
To define the relationship between Customer and Product Usage, you must create the Product Usage property in the Customer class. The Customer class represents the individual customers in the system, and by adding the Product Usage property to this class, you can associate each customer with their product usage. This allows you to track and analyze how each customer interacts with the products.