Which role authorizes budget for a service in a service relationship?

The sponsor is the role that authorizes the budget for a service, so option C is correct. In ITIL, different stakeholders in a service relationship have different responsibilities. The customer defines requirements and is accountable for the outcomes of service consumption. Users are the people who actually use the service. The sponsor is the person or group that authorizes funding and provides financial support for the service. This role is important because value co-creation depends not only on usage and outcomes, but also on the commitment of resources needed to obtain and sustain the service. A product vendor may provide or support a product, but that does not automatically make them the budget authority in the consumer organization. Therefore, the sponsor is the role most clearly linked to budget authorization.