The correct answer is D. MS DOS.
MS-DOS (Microsoft Disk Operating System) is a single-tasking operating system, which means that it can only run one program at a time. This is in contrast to multitasking operating systems, which can run multiple programs at the same time.
Windows 98, Windows NT, and Windows XP are all multitasking operating systems. They can run multiple programs at the same time by using a technique called time slicing. Time slicing divides the available processing time into small slices, and each program is given a slice of time to run. This process is repeated very quickly, so it appears that all of the programs are running at the same time.
MS-DOS does not use time slicing. Instead, it uses a technique called cooperative multitasking. In cooperative multitasking, each program is responsible for giving up control to the operating system when it is finished with its turn to run. If a program does not give up control, the operating system cannot run any other programs. This can lead to programs freezing or locking up.
In conclusion, MS-DOS is a single-tasking operating system, while Windows 98, Windows NT, and Windows XP are all multitasking operating systems.