Explanation:

GML stands for 'Generalized Markup Language' or 'GameMaker Language', neither of which is an operating system. GML (Generalized Markup Language) is a precursor to SGML and XML, used for document formatting. Options (1) 'UNIX', (2) 'MS-DOS', and (3) 'LINUX' are all well-known examples of operating systems. UNIX is a family of multitasking OS, MS-DOS is a command-line OS, and LINUX is an open-source Unix-like OS.