The correct answer is D because a walkthrough test is well suited for explaining and validating roles, responsibilities, communication flows, and expected actions among participants, including end users. In an incident response context, end users often play an important role in identifying suspicious activity, reporting incidents quickly, avoiding further damage, and following escalation instructions. A walkthrough allows participants to step through a scenario and discuss what actions should be taken at each stage. This makes it effective for communicating responsibilities and improving understanding. A parallel test is more commonly associated with running alternate processes or systems alongside normal operations. A complete failover test is more technical and disruptive, typically used for disaster recovery or continuity validation. A checklist test may confirm whether documented items exist, but it is less effective for communicating practical roles and expectations. CISM emphasizes awareness, training, testing, and role clarity as key enablers of timely incident identification and response.