The first step in an incident response plan is typically preparation12. However, among the options provided, validating the incident would be the first step. This involves confirming that a security event is actually an incident3. It's important to verify the event to avoid wasting resources on false positives. References: Incident Response Plan: Frameworks and Steps - CrowdStrike What is Incident Response? Plan and Steps | Microsoft Security What Are the Phases of an Incident Response Plan? - ISC2 Blog