Comprehensive and Detailed 200 to 250 words of Explanation From Exact Extract of project-programme-and-portfolio-management of 5th Edition MSP:

The 'Plan progressive delivery' process is the stage where the programme moves from high-level concepts to tangible, resourced plans. A key requirement of this process is to ensure that the resources (people, assets, and funding) required for the first tranche are not just identified, but actually committed by the business owners.

Option A is the correct answer. According to MSP 5th Edition, a programme should not proceed into a delivery tranche (such as Tranche 1) until there is a firm commitment from the functional managers who "own" the resources. The Call Centre Manager is the person who must balance the needs of the programme against the needs of business-as-usual (BAU). If they do not commit the staff during the planning process, the programme risks failing in its first tranche due to resource shortages. The Sponsoring Group (Option C) provides the high-level mandate and funding, but the actual day-to-day commitment of staff must come from the operational line managers. This commitment is a prerequisite for the SRO to "Agree to proceed." Obtaining this commitment early is a critical success factor for programme management, as it reduces the risk of conflict between the programme and the business once delivery starts.