Which of the Following Is Not a Primary Source of Ad

Multiple Choice

Which of the following is not a primary source of ad fraud?

A) browser extensions that insert ads into a premium publisher's website and then list the ads as available on a programmatic ad exchange
B) ad targeting firms that create bots that imitate the behavior of real shoppers and then charge advertisers
C) botnets hired by publishers to click on web pages to create phony traffic
D) native advertising that is displayed on a social media site