A team cannot complete work because requirements are unclear and hasn't finished an iteration for months. What should the project leader do to help?

The correct answer is recommending the product owner review the backlog refinement process. Unclear requirements directly indicate a problem with how the product backlog is being managed and refined. The Product Owner is responsible for maximizing the value of the product and managing the Product Backlog, which includes ensuring requirements are clear, concise, and understood by the development team. If requirements are unclear, the team cannot effectively plan or complete work, leading to stalled iterations. Reviewing iteration length with stakeholders might be a symptom of the problem, but it doesn't address the root cause of unclear requirements. Limiting work in progress (WIP) is a good practice for flow, but it won't resolve the fundamental issue of undefined work. Reviewing individual team members' performance is inappropriate; the problem lies with the clarity of work, not necessarily individual capability.