正解:A
The audit team's approach is in line with recommended auditing practices, making option A the correct answer. ISO management system audits, including ISO/IEC 27001 audits, are designed to provide reasonable assurance, not absolute assurance, that the management system conforms to the standard requirements. This principle is explicitly supported by ISO 19011 and ISO/IEC 17021-1.
In the scenario, the audit team assessed conformity by reviewing key processes, questioning responsible personnel, examining representative evidence, and evaluating control effectiveness. Although access to IT systems was limited, the auditors compensated by gathering sufficient and appropriate evidence through alternative means. This approach reflects the reality of auditing complex environments, particularly those involving third-party service providers.
Option B is incorrect because ISO standards do not require auditors to assess every process in full detail.
Audits are sample-based by design. Expecting a complete, exhaustive assessment of each process would be impractical and inconsistent with audit principles. Option C is incorrect because assessing the ISMS as a whole is not merely an efficiency-driven decision; it is an accepted and intentional audit approach aimed at evaluating system-level effectiveness.
Therefore, obtaining reasonable assurance through a structured, evidence-based approach confirms that the audit team acted in accordance with recommended audit practices.