In the text mining approach to detecting spam we ignored all attachments in creating the set of words belonging to a message (see Section 3.5.2). Write a function to extract words from any plain text or HTML attachment and include these words in the set of a message's words. Try to reuse the find Msg () function and modify the drop Attach () function to accept an additional parameter that indicates whether or not the words in attachments are to be extracted. Does this change improve the classification?