Which of the following is NOT an example of an operating system?

The correct choice highlights that Photoshop is not an operating system. An operating system (OS) serves as the primary software that manages computer hardware and software resources and provides common services for computer programs. Examples of operating systems include Windows, macOS, and Linux, all of which serve as platforms upon which applications can run and manage system resources.

Photoshop, on the other hand, is a graphic design and photo editing application. While it functions on various operating systems like Windows and macOS, it does not perform the fundamental tasks of managing hardware and software resources. Instead, it relies on an operating system to operate and provide the necessary interfaces for the user. Hence, it is categorized separately from the other options, which are indeed operating systems.