An experienced agile team cannot finish estimates during backlog refinement because key information is missing. What should the project manager do?

The correct answer is to ask the product owner to review the stories with stakeholders prior to planning. In agile, the product owner is responsible for maximizing the value of the product and managing the product backlog, which includes ensuring stories are well-defined and understood. If key information is missing for estimation, the product owner needs to collaborate with stakeholders to gather the necessary details and clarify requirements before the team can accurately estimate. Postponing iteration planning (A) is a reactive measure that delays progress without addressing the root cause. Reviewing the project backlog with the product owner (C) is part of backlog refinement, but the issue here is missing external information, not just internal review. Using previous project estimates (D) is inappropriate because each story is unique and requires specific understanding for accurate estimation; using old estimates can lead to significant inaccuracies.