The correct answer is C.
Choices A, B, and D are processes in the monitoring and controlling process group. This situation asks how to prevent the problem. This would have been done during the planning processes. The project deliverables are defined in the Define Scope process (choice C), which is a part of project planning. Good planning reduces the likelihood of a situation like the one described by including the right people and spending adequate time in clarifying the project scope.
Pass PMP in the First Attempt : PMP Strategy
Revise Scope Management Concepts: Project Scope Management
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20 Questions Challenge
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