During execution, any addition to scope must go through the formal change control process. The project manager should initiate a change request for proper evaluation and approval. This ensures that scope, budget, and schedule impacts are assessed before proceeding.
According to the PMBOK Guide - Seventh Edition, any changes to the baseline during execution must follow the change control procedures defined in the governance structure.
Option A risks scope creep.
Option B is helpful but not sufficient as a next step.
Option C closes the door without considering the critical nature of the request.
References:
PMBOK Guide - Seventh Edition, Delivery and Planning Performance Domains PMI Change Control and Governance Guidelines