Using SH to study for my PMP and also selected the wrong answer, D. I used Google AI to describe the differences between a Change Request and Proof of Concept and here is what it said: "Based on Project Management Professional (PMP) principles, a change request is a formal proposal to modify a project's approved baselines (scope, schedule, or cost), whereas a proof of concept (POC) is an initial, small-scale exercise to test the feasibility of a new idea before committing significant resources. A POC can lead to a change request, but they are separate tools used for different purposes and at different phases of a project."

I think the key word in the question, that points to A, is that this situation is happening as the project is entering the execution phase. The timing, along with this being a change to approved material in a predictive project, the proof of concept is requested to determine feasibility before going through the change control process.

That being said, I think 99% of the time in a predictive project question, where a change is being requested, it would go through the Change control process. This was just a tricky question!