As a project nears completion, the project manager finds out that several key members of the project team have been reassigned to other projects. If the scope and schedule of the project stay the same

If key team members are reassigned and the project's scope and schedule remain fixed, the project's cost will almost certainly change, most likely increasing. This is because the project manager will need to either replace the departed members, potentially with more expensive temporary staff or contractors, or pay overtime to the remaining team members to maintain the original schedule and scope.

While quality could be affected, quality metrics themselves are measures; the question asks what will change, and cost is a more direct and certain impact if scope and schedule are fixed and resources are lost.

Key Performance Indicators (KPIs) are measures of performance; while performance might be impacted, the KPIs themselves do not change, but the project's ability to meet them might.

Work performance refers to how well the team is executing tasks; while it might be negatively impacted, "cost" is a more fundamental and directly quantifiable change when resources are removed but output requirements remain.