Which relationship must be established with an external system or a service provider before creating...

 A usage subscription is a relationship between a service point and an external system or a service provider that defines how usage data is exchanged and processed1. A usage subscription is required before creating bill determinants, as it determines the usage calculation group, the usage transaction type, and the usage subscription quantity type that are used to derive bill determinants from usage data2. A usage subscription also specifies the usage rule that is used to request bill determinants from the external system or the service provider3. Therefore, the correct answer is C. Usage Subscription. References:

Understanding Usage Subscriptions

Creating Usage Subscriptions

Requesting Bill Determinants