A law firm uses Office 365 for email and document collaboration. Which cloud service model is this?

SaaS (Software as a Service) is correct because Office 365 is a complete, ready-to-use software application delivered over the internet. Users access it via a web browser or client application without managing the underlying infrastructure (servers, operating systems, or network). The law firm consumes the software directly. PaaS (Platform as a Service) provides a platform for developers to build, run, and manage applications without the complexity of building and maintaining the infrastructure typically associated with developing and launching an app. IaaS (Infrastructure as a Service) provides virtualized computing resources over the internet, giving users control over operating systems, applications, and middleware, but not the underlying physical infrastructure. FaaS (Function as a Service) is a serverless execution model where developers write and deploy small, single-purpose functions that run in response to events, without managing servers.