The correct answer is C because the scenario requires disciplined procurement and supplier management rather than an immediate, informal, or purely administrative reaction. The selected response - C. Propose outsourcing part of the project to a third-party supplier. - directly addresses the condition described in the question and keeps the project aligned with authorized objectives. PMBOK-aligned practice requires the project manager to assess supplier capability, contract impact, cost, quality, schedule, and available alternatives before committing project resources. 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: business environment, procurement and supplier management, stakeholder communication, impact analysis, governance, value delivery, and continuous improvement.