The primary purpose of obtaining a baseline image during an operating system audit is to identify atypical running processes. A baseline image is a snapshot of the normal state and configuration of an operating system, including the processes that are expected to run on it. By comparing the current state of the operating system with the baseline image, an IS auditor can detect any deviations or anomalies that may indicate unauthorized or malicious activity, such as malware infection, privilege escalation, or data exfiltration. A baseline image can also help an IS auditor to assess the performance and efficiency of the operating system, as well as its compliance with security standards and policies.
Verifying antivirus definitions (option B) is not the primary purpose of obtaining a baseline image, although it may be a part of the baseline configuration. Antivirus definitions are the files that contain the signatures and rules for detecting and removing malware. An IS auditor may verify that the antivirus definitions are up to date and consistent across the operating system, but this does not require obtaining a baseline image.
Identifying local administrator account access (option C) is not the primary purpose of obtaining a baseline image, although it may be a part of the baseline configuration. Local administrator accounts are user accounts that have full control over the operating system and its resources. An IS auditor may identify and review the local administrator accounts to ensure that they are properly secured and authorized, but this does not require obtaining a baseline image.
Verifying the integrity of operating system backups (option D) is not the primary purpose of obtaining a baseline image, although it may be a part of the backup process. Operating system backups are copies of the operating system data and settings that can be used to restore the system in case of failure or disaster. An IS auditor may verify that the operating system backups are complete, accurate, and accessible, but this does not require obtaining a baseline image.
References: : Linux security and system hardening checklist : CISA Certification | Certified Information Systems Auditor | ISACA : CISA Certified Information Systems Auditor Study Guide, 4th Edition : CISA - Certified Information Systems Auditor Study Guide [Book]

Reviewing and evaluating application test cases is the most effective use of an IS auditor's time during the evaluation of controls over a major application development project. Application test cases are designed to verify that the application meets the functional and non-functional requirements and specifications. They also help to identify and correct any errors, defects, or vulnerabilities in the application before it is deployed. By reviewing and evaluating the test cases, the IS auditor can assess the quality, reliability, security, and performance of the application and provide recommendations for improvement.

Recent third-party IS audit reports would be most helpful in determining the effectiveness of the IT governance framework of the target company. IT governance is a framework that defines the roles, responsibilities, and processes for aligning IT strategy with business strategy. A third-party IS audit is an independent and objective examination of an organization's IT governance framework by an external auditor.
Recent third-party IS audit reports can provide reliable and unbiased evidence of the strengths, weaknesses, and maturity of the IT governance framework of the target company. The other options are not as helpful as recent third-party IS audit reports, as they may not be as comprehensive, accurate, or current as external audits. References: CISA Review Manual, 27th Edition, page 94

The IS auditor's first action after discovering an option in a database that allows the administrator to directly modify any table should be to determine whether the audit trail is secured and reviewed. This is because direct modification of database tables can pose a significant risk to data integrity, security, and accountability. An audit trail is a record of all changes made to database tables, including who made them, when they were made, and what was changed. An audit trail can help to detect unauthorized or erroneous changes, provide evidence for investigations or audits, and support data recovery or restoration. The IS auditor should assess whether the audit trail is protected from tampering or deletion, and whether it is regularly reviewed for anomalies or exceptions.