Kubernetes supports multiple virtual clusters backed by the same physical cluster. These virtual clusters are called:

Kubernetes uses Namespaces to create logical partitions or "virtual clusters" within a single physical cluster. Namespaces provide a scope for resource names, ensuring that names of objects like Pods, Services, and Deployments are unique within a namespace but can be reused across different namespaces. They are the primary mechanism for isolating resources for different teams, projects, or environments, and for applying resource quotas and access control policies (RBAC) to a subset of the cluster, effectively simulating a multi-tenant environment.

B. Containers are the runtime units for applications, not a mechanism for partitioning a cluster.
C. Hypervisors are low-level software that create and run virtual machines, operating below the Kubernetes layer.
D. cgroups are a Linux kernel feature for resource limiting processes; they are a building block for containers, not a Kubernetes cluster-level abstraction.

1. Kubernetes Documentation. (n.d.). Concepts > Working with Objects > Namespaces. Retrieved from https://kubernetes.io/docs/concepts/overview/working-with-objects/namespaces/. The documentation states, "Kubernetes supports multiple virtual clusters backed by the same physical cluster. These virtual clusters are called namespaces."

2. The Linux Foundation. (2021). LFS258: Kubernetes Fundamentals. Chapter 13, Section 13.1, "Namespaces". This section explains that namespaces are used to organize objects in a cluster and provide a scope for names, effectively creating isolated environments.