In the Act phase of the PDCA cycle, the process is reviewed and evaluated based on the results from the Check phase. The actions taken in this phase aim to continually improve the process performance by addressing the root causes of problems, implementing corrective and preventive actions, and updating the process documentation1. Reference: ISO/IEC 27001:2022 Lead Auditor (Information Security Management Systems) | CQI | IRCA

The appropriate actions to take next are to investigate whether pest infestation is an identified risk and if so, what risk treatment is to be applied, to determine whether the high levels of rainfall have had other impacts on data centre operations, and to check with the guide that they intend to initiate the organisation's information security incident process. These actions are relevant to the ISMS audit objectives and criteria, as they relate to the organisation's risk assessment and treatment, security performance, and incident management processes. The other actions are either not within the scope of the ISMS audit, not required by the ISO/IEC 27001 standard, or not the responsibility of the auditor. Reference: PECB Candidate Handbook1, page 21-22; ISO/IEC 27001:2022 (en)2, clauses 6.1, 8.2, 9.1, and 10.2.

The correct response is A, because grading criteria provide a common basis for the evaluation of nonconformities across the organization. Grading criteria are the rules or standards that define the severity or impact of nonconformities, and help to determine the appropriate corrective actions and follow-up activities.
Grading criteria are important for several reasons, such as:
* They ensure consistency and objectivity in the assessment and reporting of nonconformities, and avoid subjective or arbitrary judgments.
* They facilitate the communication and understanding of nonconformities among the auditors, the auditees, and the audit clients, and enable the comparison and benchmarking of nonconformities across different processes, functions, or locations.
* They support the prioritization and allocation of resources for the resolution of nonconformities, and the monitoring and measurement of the effectiveness of the corrective actions.
* They demonstrate the commitment and accountability of the organization to the continual improvement of the ISMS, and the compliance with the ISMS requirements and expectations.
References:
* ISO/IEC 27001:2022, Information technology - Security techniques - Information security management systems - Requirements1
* PECB Candidate Handbook ISO/IEC 27001 Lead Auditor2
* ISO 27001:2022 Lead Auditor - PECB3
* ISO 27001:2022 certified ISMS lead auditor - Jisc4
* ISO/IEC 27001:2022 Lead Auditor Transition Training Course5
* ISO 27001 - Information Security Lead Auditor Course - PwC Training Academy
* ISO 19011:2022, Guidelines for auditing management systems

A first-party audit is an internal audit conducted by the organization itself or by an external party on its behalf. The objectives of a first-party audit are to: 12
* Confirm the scope of the management system is accurate, i.e., it covers all the processes, activities, locations, and functions that are relevant to the information security objectives and requirements of the organization.
* Update the management policy, i.e., review and revise the policy statement, roles and responsibilities, and objectives and targets of the information security management system (ISMS) based on the audit findings and feedback.
The other phrases are not objectives of a first-party audit, but rather:
* Apply international standards: This is a requirement for the ISMS, not an objective of the audit. The ISMS must conform to the ISO/IEC 27001 standard and any other applicable standards or regulations12
* Prepare the audit report for the certification body: This is an activity of a third-party audit, not a first- party audit. A third-party audit is an external audit conducted by an independent certification body to verify the conformity and effectiveness of the ISMS and to issue a certificate of compliance12
* Complete the audit on time: This is a performance indicator, not an objective of the audit. The audit should be completed within the planned time frame and budget, but this is not the primary purpose of the audit12
* Apply regulatory requirements: This is also a requirement for the ISMS, not an objective of the audit. The ISMS must comply with the legal and contractual obligations of the organization regarding information security12 References:
1: ISO/IEC 27001:2022 Lead Auditor (Information Security Management Systems) Course by CQI and IRCA Certified Training 1 2: ISO/IEC 27001 Lead Auditor Training Course by PECB 2