Which of the following is not a filter command? A. sort B. wc C. grep D. cat E. None of the above

The correct answer is: D. cat

A filter command is a command that

sort sorts the lines of a file in alphabetical or numerical order.
wc counts the number of lines, words, and characters in a file.
grep searches a file for lines that match a regular expression.
cat concatenates files or standard input and prints them to standard output.

cat is not a filter command because it does not produce output based on any criteria. It simply prints the contents of a file or standard input to standard output.