Senior management support is essential to ensuring effective incident response because it provides the necessary authority, resources, and guidance for the information security team to perform their roles and responsibilities. Senior management support also helps to establish the goals, scope, policies, and procedures for the incident response plan (IRP), as well as to ensure its alignment with the business objectives and strategy. Senior management support also fosters a culture of security awareness, accountability, and collaboration among all stakeholders involved in the incident response process.

The other options are not essential to ensuring effective incident response, although they may be helpful or beneficial. A business continuity plan (BCP) is a document that outlines the actions and arrangements to ensure the continuity of critical business functions in the event of a disruption or disaster. A cost-benefit analysis is a method of comparing the costs and benefits of different alternatives or solutions to a problem. A classification scheme is a system of categorizing information assets based on their sensitivity, value, and criticality.

References = CISM Manual1, Chapter 6: Incident Response Planning (IRP), Section 6.1: Incident Response Plan2

1: https://store.isaca.org/s/store#/store/browse/cat/a2D4w00000Ac6NNEAZ/tiles 2: 4