Answer:
B. Computer operating system
Explanation:
the operating system (or OS) manages all of the hardware and software in the computer, and allows hardware and software to communicate.
We can also figure this out by process of elimination: Application software is just a fancy way to say apps, Graphical User Interface (or GUI) are menus that allow a user to use the computer through a visual representation (what you interact with using your mouse), and microcomputer just means a small computer like a laptop or a phone.
