Suppose a cloud contains software stack such as Operating System, Application software, etc. This model is referred as _____ model.

Explanation

The official key marks SaaS (Software as a Service), the delivery model in which the provider hosts the whole software stack, including the operating system and the application software, and the consumer simply uses the finished application over the network. IaaS supplies only the raw compute, storage and network on which the customer installs its own stack, PaaS supplies a runtime and development platform but not the finished application, and MaaS (Monitoring as a Service) is unrelated. Because the question stresses that the cloud already contains the ready application software, the intended answer is the topmost service layer, SaaS.