New PMP Question & Answers with explanation

A stakeholder believes that a recent project's deliverables were not achieved. What should the project manager do to gain this stakeholder's approval?
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A project manager receives a chain of emails from the project team and vendor arguing about a recently received deliverable. The project team believes that the deliverable fails to meet a specific requirement, but the vendor maintains that they are unaware of this requirement. To what should the project manager first refer?
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A project manager is leading a 12-month project to deliver a new product to market. The project sponsor wants to narrow the scope and deliver a scaled-down version of the final product. What will the project manager require prior to changing the scope?
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An important product feature was not documented during project planning. The customer notices the error during the second deliverable review. What should the project manager do?
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