Answer: c. by the content and how frequently others link to you
Explanation: To make it simple without overcomplicating the stuff:
The search engine looks at the website and checks how is the website matching the search.
Reviews/referral's: If other website links your website this increases the website's credibility.
Website visitors and domain authority: If users or visitors clicks the website link and took some time on your website this gives a good impression for the site which will let the website be suggested.
Search engines also see how your website is trustable and reliable based on the overall content and quality.