Answer:
Option A: Software-as-a-service
Step-by-step explanation:
Software-as-a-service (SAAS) is one of the cloud computing business models. The software is not delivered as a product hosted in the client machine. Instead, a customer just pays a subscription fee (sometimes free for limited quota) to gain access to the software which is hosted in a remote server maintainer by software vendor.
One benefit of SAAS is that the software vendor will usually responsible for software maintenance and update. The customer has no longer require to pay extra cost to upgrade the software. So long as the subscription is still valid, a customer can always access to the newest features of software.
Some examples of SAAS which is popular include DropBox, Google App, DocuSign, Microsoft Office 365 etc.