Which software development approach ensures that application and platform requirements are frequently tested for immediate availability?

The correct answer focuses on Continuous Delivery as it is a software development practice where code changes are automatically prepared for a release to production. This approach emphasizes ensuring that every change made to the application is thoroughly tested and can be deployed to production quickly and reliably, often on-demand.

In Continuous Delivery, automation plays a key role in allowing teams to frequently test and validate the application against current requirements, thereby ensuring immediate availability of the application features or updates to users. This process helps in catching issues early and facilitates a more flexible response to changing requirements or feedback, thus maintaining the quality of the software package while preparing for deployment.

While Continuous Integration does involve integrating code changes frequently and running tests, its primary focus is on merging code changes into a shared repository regularly. Continuous Deployment, on the other hand, takes things further than Continuous Delivery by automatically deploying every change passed through the testing stage directly to production without requiring explicit approval, but the essence of regularly validating readiness for deployment is best encapsulated by Continuous Delivery. In contrast, the Waterfall Model follows a more traditional approach of distinct phases in software development and lacks the iterative feedback loop present in the other methodologies.