Although the Stakeholder(s) and the Product Owner have the final say on Prioritized Product Backlog Items and whether to accept or reject any Change Requests presented during Demonstrate and Validate Sprint, it is the Scrum Master's responsibility to ensure that the requirements and Acceptance Criteria are not altered during the Sprint Review Meeting for the User Stories completed in the current Sprint. This prevents the rejection of completed User Stories based on the fact that they do not meet newly changed requirements. If any requirements need to be changed, any corresponding PBI needs to be revised to accommodate the modified requirements in a future Sprint.