The correct answer is: D. a layer of software.
A virtual machine monitor (VMM) is a layer of software that creates and runs virtual machines. It is also known as a hypervisor. A VMM provides the illusion of a physical machine to each virtual machine, including its own CPU, memory, storage, and network interface. This allows multiple operating systems to run simultaneously on a single physical machine.
A virtual machine is a software program that creates a simulated computer environment. It can be used to run multiple operating systems on a single physical machine, or to test software in a sandbox environment.
Hardware is the physical components of a computer system, such as the CPU, memory, storage, and network interface.
A host operating system is the operating system that runs on the physical machine that hosts the virtual machines.
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