Answer:
c. spiders
Explanation:
Search engine spiders, sometimes referred to as web crawlers, are web bots used by Internet search engines to gather information about Web sites and individual Web pages. The search engines need to get information from all the sites and pages online; otherwise they wouldn't identify the pages to display in response to a search query or with what level of priority.
Think of the process this way. anytime you search something on Google or Yahoo or Bing, those pages and pages of results can't just materialize and come out to your screen of thin air, they’ve been indexed by these search engine crawlers and will display those pages to you anytime you search on something relevant to them.