Trick question!
Desktop and mouse are NOT a part of the operating system. They are operating system although mac is the only one to use a one button mouse
The GUI and finder feature are only used with apple but the apple operating system is built on top of the unix operating system. Similar to Linux and other systems that do have similar features but just with different names.
If the question was what sets apple systems apart from others it would be the mouse with the one button.
