Input validation is the best control to address SQL injection vulnerabilities, because it can prevent malicious users from entering SQL commands or statements into input fields that are intended for data entry, such as usernames or passwords. SQL injection is a technique that exploits a security vulnerability in an application's software by inserting SQL code into a query string that can execute commands on a database server. Unicode translation, SSL encryption, and digital signatures are not effectivecontrols against SQL injection, because they do not prevent or detect SQL code injection into input fields. References: CISA Review Manual (Digital Version), Chapter 5, Section 5.4.2

Automated version control systems are the best method to maintain an audit trail of changes made to the source code of a program. They automatically track and manage changes to the source code over time, allowing you to see what changes were made, when they were made, and who made them1. This provides a clear and detailed audit trail that can be invaluable for debugging, understanding the evolution of the code, and ensuring accountability23.

The primary benefit of information asset classification is that it enables risk management decisions.
Information asset classification helps to identify the value, sensitivity and criticality of information assets, and to determine the appropriate level of protection and controls required for them. This facilitates risk assessment and risk treatment processes, and ensures that information assets are aligned with business objectives and regulatory requirements. Preventing loss of assets, helping to align organizational objectives or facilitating budgeting accuracy are secondary benefits of information asset classification, but not the main purpose. References: ISACA, CISA Review Manual, 27th Edition, 2018, page 300

The IS auditor's independence would be most likely impaired if they implemented a specific control during the development of an application system. This is because the IS auditor would be auditing their own work, which creates a self-review threat that could compromise their objectivity and impartiality. The IS auditor should avoid participating in any operational or management activities that could affect their ability to perform an unbiased audit. The other options do not pose a significant threat to the IS auditor's independence, as long as they follow the ethical standards and guidelines of the profession.