A set of nodes that cooperate to run containerized applications under Kubernetes control is the correct description of a Kubernetes cluster.

The phrase a set of nodes that cooperate to run containerized applications under Kubernetes control captures the core idea because a cluster is made of machines or virtual machines that act as nodes and they work together to host pods and containers under the management of the control plane and kubelet agents.

A Kubernetes cluster includes the control plane components that schedule work and maintain cluster state and it includes worker nodes that run the containerized workloads and provide networking and storage resources for pods.

A group of linked servers used mainly for serving websites is incorrect because a Kubernetes cluster is not defined by the type of applications it runs or by a single purpose such as serving websites.

A collection of containers that all use the same IP address is incorrect because a cluster is about the nodes and orchestration rather than a group of containers sharing an IP address, and containers in Kubernetes run inside pods which have their own networking model.

Google Kubernetes Engine is incorrect because it is a managed Kubernetes service offered by Google and not a definition of what a cluster is. It is a product that creates and manages clusters rather than being the conceptual description of a cluster.

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