The best way to ensure that potential security issues are considered by the development team as part of incremental changes to agile-developed software is to include a mandatory step to analyze the security impact when making changes. This will help to identify and mitigate any security risks or vulnerabilities that may arise from the changes, and to ensure that the software meets the security requirements and standards. The other options are not as effective, because they either delegate the security analysis to someone outside the development team, rely on post-deployment testing, or focus on documentation rather than analysis.
References: CISA Review Manual (Digital Version)1, Chapter 4, Section 4.2.5