The correct answer is A because the scenario requires disciplined stakeholder engagement rather than an immediate, informal, or purely administrative reaction. The selected response - A. Update the stakeholder register and provide a tailored onboarding session for the new stakeholder. - directly addresses the condition described in the question and keeps the project aligned with authorized objectives. PMBOK-aligned practice requires the project manager to clarify expectations, preserve transparency, and use the appropriate decision or communication channel. This is especially important when project constraints, stakeholder expectations, quality expectations, delivery cadence, or business value may be affected. The competing options are weaker because they either bypass the accountable role, defer action without analysis, escalate before the project manager has prepared decision-quality information, or solve a symptom without correcting the underlying process issue. The selected answer also preserves transparency, ownership, and traceability, which are essential for sound project governance and effective delivery. PMBOK Guide Eighth Edition topics: people, stakeholder engagement, stakeholder communication, impact analysis, governance, value delivery, and continuous improvement.