An online service provider provides Jeannie and her team with hosted computers, an operating system, and a database management system $($DBMS$).$ This allows Jeannie and her team to add their own applications to the hosted services. Which of the following cloud$-$based offerings is being provided to the users?

platform as a service $($PaaS$)$

unified communications as a service $($UCaaS$)$

infrastructure as a service $($laaS$)$

software as a service $($SaaS$)$