While working with MS-DOS which command is used to change the extension of all filenames ending with .txt to .doc? A. Ren *.doc *.txt B. Ren *.txt *.doc C. Ren file.doc file.txt D. Ren a: *.doc *.txt

The correct answer is A. Ren .doc .txt.

The Ren command is used to rename files. The asterisk () is a wildcard character that matches any number of characters. So, the command Ren .doc *.txt will rename all files that end in .doc to .txt.

Option B would rename all files that end in .txt to .doc. This is not what is asked for in the question.

Option C would rename the file file.doc to file.txt. This is not what is asked for in the question.

Option D would rename all files on the A: drive that end in .doc to .txt. This is not what is asked for in the question.