The sustainability plan ensures results are reinforced and maintained after initial adoption. ACMP explains that this plan integrates reinforcement mechanisms, monitoring adoption, aligning performance management, and recognizing behaviors. Transition plans (A) handle operational handoffs, stakeholder engagement (B) supports involvement, and human resource plans (D) address capacity. To ensure outcomes are sustained, the correct plan is the sustainability plan (C).

(Reference: ACMP Standard, Process Group 4 -- Execute; Sustainability Plan ensures long-term adoption and embedding into operations.)