C. Capture stakeholder expectations, and revise the stakeholder engagement plan.
In this situation, where key stakeholders are concerned about their lack of involvement and understanding of the program's benefits, the program manager should actively engage with these stakeholders to capture their expectations and concerns. Following this, the program manager should revise the stakeholder engagement plan to address these concerns. This plan is a strategic document that outlines how stakeholders will be engaged and communicated with throughout the program. By revising this plan to include more regular and targeted engagement activities for the concerned stakeholders, the program manager can ensure that they are kept informed and their needs are addressed. This approach not only alleviates their concerns but also helps in gaining their support and buy-in for the program.