A vendor requires privileged access to a key business application. The best recommendation to reduce the risk of data leakage is to implement real-time activity monitoring for privileged roles. This is because real-time activity monitoring can provide visibility and accountability for the actions performed by the vendor with privileged access, such as creating, modifying, deleting, or copying data. Real-time activity monitoring can also enable timely detection and response to any unauthorized or suspicious activities that may indicate data leakage. Including the right-to-audit in the vendor contract is a good practice, but it may not be sufficient to prevent or detect data leakage in a timely manner, as audits are usually performed periodically or on-demand.
Performing a review of privileged roles and responsibilities is also a good practice, but it may not address the specific risk of data leakage by the vendor with privileged access. Requiring the vendor to implement job rotation for privileged roles may reduce the risk of collusion or fraud, but it may not prevent or detect data leakage by any individual with privileged access. References: CISA Review Manual (Digital Version),
[ISACA Privacy Principles and Program Management Guide]

An IS auditor should be consulted during the requirements definition phase to recommend security controls.
This ensures that security considerations are integrated from the beginning of the software development life cycle, leading to more secure software design and implementation.
References
* ISACA CISA Review Manual 27th Edition, Page 240-241 (SDLC Phases)

Secure code reviews as part of a continuous deployment program are preventive controls. Preventive controls are controls that aim to prevent or avoid undesirable events or outcomes from occurring, such as errors, defects, or incidents. Secure code reviews are activities that examine and evaluate the source code of a software or application to identify and eliminate any vulnerabilities, flaws, or weaknesses that may compromise its security, functionality, or performance. Secure code reviews as part of a continuous deployment program can help prevent or avoid security issues or incidents from occurring by ensuring that the code is secure and compliant before it is deployed to production. The other options are not correct types of controls for secure code reviews as part of a continuous deployment program, as they have different meanings and functions. Detective controls are controls that aim to detect or discover undesirable events or outcomes that have occurred, such as errors, defects, or incidents. Logical controls are controls that use software or hardware mechanisms to regulate or restrict access to IT resources, such as data, systems, or networks.
Corrective controls are controls that aim to correct or rectify undesirable events or outcomes that have occurred, such as errors, defects, or incidents. References: CISA Review Manual (Digital Version), Chapter 3, Section 3.2

The best way to evaluate the effectiveness of a newly developed application is to review acceptance testing results. Acceptance testing is a process of verifying that the application meets the specified requirements and expectations of the users and stakeholders. Acceptance testing results can provide evidence of the functionality, usability, reliability, performance, security and quality of the application. Performing a post-implementation review, analyzing load testing results, and performing a secure code review are also important activities for evaluating an application, but they are not as comprehensive or conclusive as acceptance testing results.
References: Info Technology & Systems Resources | COBIT, Risk, Governance ... - ISACA, IT Governance and Process Maturity