Google Apps is a set of online applications allowing users to create and share documents and spreadsheets. This is an example of:

Platform as a Service (PaaS) provides a platform for developers to build, run, and manage applications, not a finished end-user application like Google Apps.

Software as a Service (SaaS) delivers applications over the internet as a ready-to-use service, where the provider manages all underlying infrastructure, platforms, and the software itself. Google Apps exemplifies SaaS as users access and use the software directly without managing any infrastructure components.

Infrastructure as a Service (IaaS) provides virtualized computing resources such as virtual machines and networks, not fully developed applications for end-users.

This choice is incorrect because Google Apps is a clear example of SaaS.