The correct answer is D. All of the above.
A backup is a copy of data that is stored in a safe location in case the original data is lost or damaged. Disk defragmentation is a process that rearranges the data on a hard drive so that it is stored in contiguous blocks, which can improve the performance of the hard drive. Virus scanning is a process that checks a computer for viruses and other malware.
All of these are important tasks that can help to keep a computer running smoothly and securely. However, they are not system tools. System tools are programs that are used to manage the operating system and other software on a computer. Some examples of system tools include the Task Manager, the Registry Editor, and the Device Manager.
The Task Manager is a program that allows users to view and manage the processes that are running on a computer. The Registry Editor is a program that allows users to view and modify the registry, which is a database that stores configuration information for the operating system and other software. The Device Manager is a program that allows users to view and manage the devices that are connected to a computer.
These are just a few examples of system tools. There are many other system tools available, and the specific tools that are available will vary depending on the operating system and the hardware configuration of the computer.