During a phase-gate review the team finds the project benefits need sponsor validation, but the sponsor recently changed and the new sponsor seems unsupportive. What should the project manager do?

The project manager's primary responsibility is to ensure project success. A new, unsupportive sponsor poses a significant threat to project benefits realization. Scheduling a one-on-one meeting is the most proactive and direct approach to address this. It allows the project manager to understand the sponsor's concerns, educate them on the project's value, and build rapport, aiming to secure their crucial buy-in. Notifying senior management immediately (Option A) might be necessary later but is premature before attempting direct engagement. Arranging a meeting to clarify the business document (Option B) is too narrow; the issue is broader than just understanding a document. Recording the change as a risk (Option D) is a good practice for documentation, but it doesn't actively resolve the immediate problem of lacking sponsor support.