Which of these cloud distribution models delivers a licensed application to customers over the Internet as an on-demand service?

Which of these cloud distribution models delivers a licensed application to customers over the Internet as an on-demand service?

• Platform as a service
• Infrastructure as a service
• Security as a service
• Software as a service 

EXPLANATION

Software as a service, or "software on demand," is a software licensing and delivery model where a vendor hosts an application and allows you to download it for a set period of time.
This can be handy if your business wants access to a particular application without the upfront costs of purchasing a full license or dealing with maintenance.