Explanation
The project manager should have ensured that communications were sent to all stakeholders when requirements change, as this is one of the key processes in the Project Communications Management knowledge area. According to the PMBOK Guide, the project manager should implement the approved actions and workarounds required to manage project risks, which may include changes to the project management plan, project documents, and organizational process assets. The project manager should also monitor and control project work to track, review, and regulate the progress and performance of the project, identify any areas in whichchanges to the plan are required, and initiate the corresponding changes. The project manager should communicate the project status, issues, risks, and changes to the relevant stakeholders, as well as obtain their feedback and input. Ensuring changing stakeholder needs and requests were properly monitored (A) is not enough, as the project manager also needs to communicate the changes to the affected stakeholders.
Ensuring project requirements were validated and communicated with the procurement team is not sufficient, as the project manager also needs to communicate the changes to the other stakeholders, such as the end users, sponsors, and senior management. Ensuring procurement contracts were able to be canceled when situations like this arise (D) is not a proactive or effective way to manage changes, as it may incur additional costs, delays, and conflicts with the vendors. References: PMBOK Guide, 6th edition, pages 368-369,
387-388, 443-444; PMP Examination Content Outline, pages 9-10, 13-14.