Answer:
d. all of the above
Explanation:
Google filetype operator enables restricting the search results to the specified file type. For example if you are searching for Eiffel Tower and you want to restrict the results to pdf files then the query will be of the form Eiffel Tower filetype:pdf . Similarly for text file results you need to specify the search query as Eiffel Tower filetype:text. The Google filetype operator supports several different file types.
