Obtaining senior management buy-in is the best way to enable the assignment of risk and control ownership because it helps to establish the authority and accountability of the risk and control owners, as well as to provide them with the necessary resources and support to perform their roles. Risk and control ownership refers to the assignment of specific responsibilities and accountabilities for managing risks and controls to individuals or groups within the organization. Obtaining senior management buy-in helps to ensure that risk and control ownership is aligned with the organizational objectives, structure, and culture, as well as to communicate the expectations and benefits of risk and control ownership to all stakeholders. Therefore, obtaining senior management buy-in is the correct answer.