The correct answer is MS-DOS. MS-DOS:DOS is a CUI type of Operating System. An operating system is system software that is loaded from disk devices when the system is started or rebooted. DOS is a single-tasking, single-user operating system with a command-line interface. Additional InformationLinux- Linux is one of popular version of UNIX operating System. It is open source as its source code is freely available. It is free to use. Linux was designed considering UNIX compatibility. It is used as a multi-tasking operating system. Unix- The Unix operating system is a set of programs that act as a link between the computer and the user. The computer programs that allocate the system resources and coordinate all the details of the computer's internals is called the operating system. Windows 7- Windows 7 is an operating system that Microsoft has produced for use on personal computers. It is the follow-up to the Windows Vista Operating System, which was released in 2006. An operating system allows your computer to manage software and perform essential tasks. Hence, the MS-DOS is not a multitasking operating system.