In the Transition phase of the Rational Unified Process (RUP), the system is deployed into the production environment, and ownership of the system is formally transferred to stakeholders. This phase involves user training, fine-tuning, and final acceptance, ensuring that the business takes responsibility for the system.

Option B (Inception): Defines the project scope and business case.

Option C (Elaboration): Focuses on refining requirements and validating architecture.

Option D (Construction): Involves building and coding the system.

Thus, system ownership is assigned to stakeholders in the Transition phase.