In project management, when a stakeholder requests a change, the project manager should ask them to submit a formal change request. This is in line with the PMBOK Guide's recommendations on Integrated Change Control. This process ensures that each change request is properly documented, evaluated, and approved or rejected by the Change Control Board (CCB). It also allows for the potential impacts on the project's triple constraints (scope, time, cost) to be assessed. In this scenario, the project manager should ask Country A to submit a change request. This request will then be analyzed along with any potential impacts on Countries B and C. References: PMBOK Guide, 6th Edition, Section 4.6: Perform Integrated Change Control