The correct answer is C. Command.com.
Command.com is a command-line interpreter that is loaded during the booting process of MS-DOS. It provides a user interface that allows users to interact with the operating system by typing commands. Command.com also contains a number of internal commands that can be used to perform tasks such as managing files, directories, and processes.
Io.sys is a system file that contains drivers for the hardware devices that are connected to the computer. Msdos.sys is a system file that contains the core code of the MS-DOS operating system. Config.sys is a configuration file that contains settings that control the way that MS-DOS boots and runs.