The correct answer is: A. BACKUP
BACKUP is a command-line utility that can be used to create backups of files and folders on a computer. It is available in all versions of DOS, including DOS 6+.
To use BACKUP, you must first specify the files or folders that you want to back up. You can do this by typing the names of the files or folders at the command prompt, or by using wildcards.
Once you have specified the files or folders that you want to back up, you must then specify the destination of the backup. You can do this by typing the name of a file or folder, or by using a drive letter and path.
If you are backing up to a file, you must specify the name of the file and the extension. The extension must be .BKF.
If you are backing up to a folder, you must specify the name of the folder and the extension. The extension must be .BKF.
You can also specify options when you use BACKUP. These options control how the backup is performed.
For example, you can use the /F option to force BACKUP to overwrite an existing backup file. You can use the /L option to create a log file of the backup operation.
For more information on using BACKUP, you can refer to the DOS documentation.