Option C is the correct choice because expanding the primary IP range of the subnet with the gcloud tool allows for the accommodation of additional VMs without disrupting existing connections or requiring extra routes. This method ensures that the subnet can support the new VMs while maintaining uninterrupted connectivity. For example, to expand the IP range of a subnet named SUBNET to /16, you would execute: gcloud compute networks subnets expand-ip-range SUBNET –region=us-central1 –prefix-length=16. Options A, B, and D are incorrect as they either cause unnecessary downtime, do not address the IP shortage in the existing subnet, or involve overly complex solutions that don't meet the requirement for seamless connectivity.