The correct answer is D. DOS.
A multitasking operating system is an operating system that allows multiple programs to run at the same time. This is done by dividing the processor time between the programs.
Windows, Linux, and Win NT are all multitasking operating systems. DOS, on the other hand, is a single-tasking operating system. This means that only one program can run at a time.
Single-tasking operating systems are less complex than multitasking operating systems. They are also less resource-intensive, which means they can run on older computers with less memory and processing power. However, single-tasking operating systems can be more difficult to use, as you need to switch between programs manually.
Multitasking operating systems are more complex than single-tasking operating systems. They are also more resource-intensive, which means they require a newer computer with more memory and processing power. However, multitasking operating systems are easier to use, as you can run multiple programs at the same time.
In conclusion, the correct answer to the question “Which of the following is not a multitasking operating system?” is D. DOS.