Correct Answer. A. Hypervisor A hypervisor allows multiple virtual machines, each with their own operating systems, to run concurrently on a single physical server, thereby maximizing resource utilization and minimizing hardware costs.
Option B is incorrect because Docker containers are used for application virtualization rather than operating system virtualization and typically share the same operating system kernel.
Option C is incorrect because a VPN is used to create a secure network connection over the internet, not for running multiple operating systems.
Option D is incorrect as a load balancer distributes incoming network traffic across multiple servers, which does not involve virtualizing operating systems.