This is the best option because it addresses the root cause of the problem, which is the unclear product requirements. By analyzing the problem with both teams, the project leader can facilitate communication, collaboration, and alignment between them. This can help to clarify the product vision, prioritize the backlog, and identify any gaps or errors in the work done so far. This can also help to improve the quality of the product and the satisfaction of the stakeholders.
The other options are not as effective because they do not address the underlying issue or they may create more problems. For example:
* B. Selecting new team members may disrupt the existing team dynamics and introduce more uncertainty and confusion. It may also delay the project and increase the cost.
* C. Demanding that the business team define final requirements may create conflict and resentment between the teams. It may also be unrealistic or impractical to expect final requirements in a complex and changing environment.
* D. Telling the teams to continue following the initial plan may result in wasted time and resources, as well as low-quality outcomes. It may also ignore the feedback and learning from the previous sprints.

In a global project using a follow-the-sun approach, it is crucial to have effective communication to ensure a smooth handover of tasks and issues between teams in different time zones. Moving working windows to increase overlap allows for real-time communication and collaboration, which can help in addressing and resolving issues more efficiently. This approach aligns with the PMBOK guide's emphasis on effective communication management in projects1.
References:
Project Communications Management According to the PMBOK1
What is the follow the sun model? Advantages + strategy - Zendesk2
What is a follow the sun model in customer support and how do you implement it - TeamSurfboard3 Proactive communication for project managers - Project Management Institute4

When work is repeatedly "nearly done" but fails iteration expectations and returns to the backlog, the most common control problem is weak adherence to the Definition of Done. The DoD is a shared, explicit quality and completeness standard that ensures increments are potentially shippable and reduces rework.
Emphasizing and reinforcing the DoD (C) addresses the systemic cause: inconsistent quality gates, missing testing, incomplete documentation, or unclear completion criteria. Updating acceptance criteria (B) can help at the user-story level, but acceptance criteria alone do not ensure the team's internal quality activities are completed (e.g., code review, unit tests, integration, security checks). Deferring fixes to the next release (A) normalizes technical debt and undermines predictability and value delivery. Extending iterations (D) masks the issue and harms cadence; it reduces transparency and does not improve quality discipline. Strengthening DoD usage improves throughput, transparency, and predictability-key agile objectives-and aligns with continuous improvement and quality management practices expected in PMP-aligned delivery.

After resolving quality issues with deliverables, it is essential for the project manager to conduct a lessons learned session. This process is part of the knowledge area of Project Quality Management, which emphasizes the importance of continuous improvement. Conducting lessons learned helps the team understand what went wrong, why it went wrong, and how similar problems can be prevented in the future. It is a proactive step to enhance the quality of future deliverables and processes.
References:
A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Seventh Edition1.
PMI Professional in Business Analysis (PMI-PBA) Reference Materials2.