Final answer:
On-demand self-service, scalability, and pay-per-use are essential characteristics of the cloud model.
Step-by-step explanation:
An essential characteristic of the cloud model is on-demand self-service. This means that users can access and manage computing resources, such as virtual machines and storage, without needing to interact with a service provider.
Another characteristic, although not listed as an option, is scalability. Cloud services can scale up or down based on demand, allowing users to easily adjust resources according to their needs.
Pay-per-use is also a common characteristic. Users only pay for the resources they use, which can be more cost-effective than traditional IT infrastructure.