A sponsor wants to add a new deliverable and asks the project manager for the most efficient way to complete it within two months. What should the project manager do?

The project manager should recommend a cost-benefit analysis because adding a new deliverable represents a significant change to the project scope. Before committing to such a change, especially with a tight deadline, it's crucial to understand the potential impact on cost, schedule, resources, and overall project objectives. This analysis helps the sponsor make an informed decision about whether the added value of the new deliverable outweighs the associated risks and costs. Telling the sponsor it's not the project manager's responsibility is unhelpful and unprofessional. Using management reserve is premature; reserves are for known-unknown risks, not for unanalyzed scope changes. Switching methodologies without proper analysis is also a drastic and potentially detrimental action.