The docker command is used to manage Docker containers, images, networks, volumes, and other resources on a Linux system. Docker is a platform that allows users to run applications in isolated environments called containers. Docker also provides networking features that allow users to create and manage networks for containers.

To delete all unused networks that are not referenced by any container, the cloud engineer can use the docker network prune command. This command will remove all networks that have no containers connected to them. The statement C is correct.

The statements A, B, and D are incorrect because they do not delete all unused networks. The docker network erase and docker network clear commands do not exist. The docker network rm command deletes a specific network by name or ID, but not all unused networks. References: [How to Manage Docker Networks]