Code review could BEST detect an in-house developer inserting malicious functions into a web-based application, because it is a process that involves examining and verifying the source code of the application for any errors, vulnerabilities, or malicious functions. Code review can help toidentify and remove any unauthorized or harmful code that the developer may have inserted, either intentionally or unintentionally, and to ensure that the application meets the quality andsecurity standards and requirements. The other options are not as effective as code review, because:

Option A: Segregation of duties is a control that involves separating the roles and responsibilities of the developer from those of the tester, the approver, and the deployer, to prevent any conflict of interest or misuse of authority. Segregation of duties can help to reduce the risk of the developer inserting malicious functions into the web-based application, but it does not detect them.

Option C: Change management is a process that involves controlling and documenting any changes to the web-based application, such as new features, enhancements, or bug fixes, to ensure that they are authorized, tested, and approved. Change management can help to track and monitor the changes that the developer may have made to the web-based application, but it does not detect the malicious functions.

Option D: Audit modules are components that are embedded in the web-based application to record and report the activities and transactions that occur within the application, such as user login, data input, or data output. Audit modules can help to audit and review the performance and functionality of the web-based application, but they do not detect the malicious functions. References = Risk and Information Systems Control Study Manual, 7th Edition, ISACA, 2020, p. 214.