In what way are online activities of people most effectively used by modern marketers?

In what way are online activities of people most effectively used by modern marketers?
A . By analyzing the logs of the web server it can be seen which products are top sellers, allowing them to optimize their marketing campaigns for those products.
B . By tagging users of social media, profiles of their online behavior can be created. These profiles are used to ask them to promote a product.
C . By tagging visitors of web pages, profiles of their online behavior can be created. These profiles are sold and used in targeted advertisement campaigns.

Answer: A