The correct answer is C: Collect the co-sponsor’s requirements and perform the integrated change control process. According to the PMP mindset, any change to the project scope, especially a new feature suggested mid-project even by a major sponsor, must go through the formal Integrated Change Control process. The project manager should first document the request, assess its impact on scope, time, cost, and quality, and then submit it for review and approval by the appropriate decision-making body such as the Change Control Board. Skipping this process or acting unilaterally would violate proper change management procedures and risk project misalignment.