The correct answer is (d), All of the above.
An operating system (OS) is a system software that manages computer hardware and software resources and provides common services for computer programs. Operating systems are found on many devices that contain a computer, such as cell phones, video game consoles, and web servers.
Windows, Linux, and Mac OS are all examples of operating systems. Windows is a proprietary operating system developed and marketed by Microsoft. Linux is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Mac OS is a Unix operating system developed and marketed by Apple Inc. since 2001.