The suggested answer is B.
To ensure stakeholders actively support an environment for constructive communication, collaboration, and continuous improvement, 'Reviews' are the most appropriate choice. Reviews involve evaluating and providing feedback on work products or deliverables, which requires active engagement and collaboration from all stakeholders. This process naturally fosters an environment of continuous improvement as feedback is used to iteratively refine and enhance the product or process. While other options like Product Roadmap or Release Plans provide strategic direction and scheduling, they don't directly engage stakeholders in the same way to ensure ongoing communication and collaboration.