You are looking at using a Software as a Solution service in Azure... (AZ-900)

Correct answer: B) Configuration of the solution.
Solution configuration: When using a SaaS service, you are generally responsible for configuring the solution according to your specific needs. This may involve setting up user accounts, defining access controls, configuring workflows and other customization options provided by the SaaS application.
Solution availability: Although the underlying infrastructure and high availability features are managed by the SaaS provider (in this case, Azure), you still have a responsibility to ensure that the use of the SaaS solution is aligned with your organization's availability and reliability requirements. This may involve configuring redundancy or failover options within the SaaS application, if available.
Responsibilities such as installing the solution and managing the solution's scalability are normally handled by the SaaS provider in a true SaaS model. Users don't need to worry about the installation process or the underlying infrastructure, as these aspects are abstracted, and the service is delivered over the internet.