The correct answer is: C. Both a and b
In MS-DOS, you can use small or capital letters of combination of both to enter a command. However, internally MS-DOS works with uppercase letters. This means that if you enter a command in lowercase letters, MS-DOS will automatically convert it to uppercase letters before executing it.
For example, if you enter the command “dir” in lowercase letters, MS-DOS will actually execute the command “DIR”. This is because all of the commands in MS-DOS are stored in uppercase letters in the system files.
There are a few exceptions to this rule. For example, the names of files and directories can be entered in either uppercase or lowercase letters. Additionally, some commands have different meanings depending on whether they are entered in uppercase or lowercase letters. For example, the command “COPY” copies a file, while the command “copy” creates a new file.
Overall, it is generally best to enter commands in uppercase letters in MS-DOS. This will help to avoid any confusion and ensure that your commands are executed correctly.