Infrastructure as a Service (IaaS)

Explanation.

Infrastructure as a Service (IaaS) is a type of cloud computing service model that provides on-demand access to computing infrastructure resources over the internet. The infrastructure resources may include virtual machines (VMs), networking, storage, and other computing resources.

Option A, "a cloud service that delivers on-demand intranet connection between sites" is incorrect because it describes a private network service rather than IaaS.

Option B, "a cloud service that delivers on-demand internet connection between sites" is also incorrect because it does not describe IaaS. It could be referring to a type of cloud service like a content delivery network (CDN) that improves internet connectivity between sites, but it is not IaaS.

Option C, "a cloud service that delivers on-demand software services on a subscription basis" is incorrect because it describes Software as a Service (SaaS) and not IaaS.

Option D, "a cloud service that delivers on-demand resources like networking and storage" is the correct description of Infrastructure as a Service. IaaS provides customers with access to computing resources such as virtual machines, storage, and networking infrastructure, allowing them to quickly scale their IT infrastructure up or down based on their needs. The cloud provider is responsible for managing the underlying hardware and infrastructure, while the customer is responsible for managing and configuring the software and operating systems running on top of the infrastructure.

In summary, option D is the correct answer as it correctly describes Infrastructure as a Service (IaaS).