An organization recently moved its custom web applications to the cloud, and it is obtaining managed services of the back-end environment as part of its subscription. Which of the following types of…

SaaS (Software as a Service) delivers fully managed, ready-to-use software applications to end users, but this scenario involves custom-developed web applications rather than a vendor-provided software product.

A CASB (Cloud Access Security Broker) is a security policy enforcement point between cloud users and cloud services, not a cloud service delivery model, and it does not describe managing back-end environments for custom applications.

IaaS (Infrastructure as a Service) provides raw virtualized compute, storage, and networking resources where the customer manages the OS and everything above it, but in this scenario the back-end environment is managed by the provider, indicating a higher abstraction level.

PaaS (Platform as a Service) is the most technically accurate answer here: the organization deployed its own custom web applications (indicating they manage the application layer) while the cloud provider manages the underlying back-end environment including runtime, middleware, OS, and infrastructure. This matches the PaaS model where developers build and run applications on a managed platform without handling the underlying infrastructure. The marked answer of CASB (B) does not fit the scenario described.