Fill the blank:'Search engines_________the internet to discover content.'

The correct answer is "crawl." Search engines use automated programs called "spiders" or "crawlers" to systematically browse the internet, following links from page to page to discover new and updated content. This process is known as crawling. Once content is discovered, it is then processed and added to the search engine's index. "Index" is incorrect because indexing happens after crawling; it's the process of organizing the discovered content. "Investigate" is too general and doesn't accurately describe the technical process search engines use to find content.