The activity described is the Lessons Learned phase of the incident management life cycle. This phase occurs after an incident has been resolved and focuses on reviewing the event and the response effort. Creating a summary for leadership that includes the "who-what-when" (a synopsis of the incident) and evaluates the effectiveness of plans is the primary purpose of this phase. The goal is to identify strengths and weaknesses in the response to improve security posture and refine the incident response plan for future events.

A. Business continuity plan: This is a proactive plan to ensure essential business functions can continue during a disruption, not a reactive review of a past security incident.
C. Forensic analysis: This is the in-depth technical investigation to gather and preserve evidence. The summary is a high-level report that uses findings from forensics, but it is not the analysis itself.
D. Incident response plan: This is the documented set of procedures to be followed during an incident. The activity described is an evaluation of that plan's performance after the fact.

1. National Institute of Standards and Technology (NIST). (2012). SP 800-61 Rev. 2, Computer Security Incident Handling Guide. Section 3.4, "Post-Incident Activity," and Section 3.4.2, "Lessons Learned," pp. 43-44. This section explicitly states that this phase involves "learning and improving" and holding a "lessons learned meeting" to discuss what happened and how to improve. The creation of a final report for management is a key output.

2. Wilson, M., & Hash, J. (2003). CSIRT Development, Establishing a Computer Security Incident Response Team. Carnegie Mellon University, Software Engineering Institute. CMU/SEI-2003-TN-001. Section 4.3, "Post-Incident Analysis," p. 19. This document describes the post-incident phase as the time to "review all available information... to determine exactly what happened, why it happened, and what can be done to prevent it from happening again."

3. University of Washington. (n.d.). T INFO 442: Information Assurance and Cybersecurity - Incident Response. Courseware. The curriculum outlines the incident response process based on the NIST framework, identifying "Post-Incident Activity (Lessons Learned)" as the final, critical phase for review and reporting.