The correct answer is D. Protected Mode.
In Protected Mode, the operating system can allocate memory to each application, preventing any one application from accessing or modifying the memory of another application. This allows multiple applications to run simultaneously without interfering with each other.
Segmented Mode is an earlier mode of operation that does not provide the same level of protection for each application. In Segmented Mode, each application is assigned a segment of memory, but the operating system does not prevent applications from accessing or modifying the memory of other applications. This can lead to problems if one application crashes or is infected with a virus.
Unprotected Mode is a mode of operation that is even less secure than Segmented Mode. In Unprotected Mode, there is no segmentation of memory, and all applications have access to all memory. This can lead to serious problems if one application crashes or is infected with a virus.
None of the above is not a valid answer.