Which of the Following Is True of Google's Discounting Scheme

Which of the following is true of Google's discounting scheme for advertisers?

A) Advertisers get incremental ten percent discounts on their original CPC for every thousand clicks.
B) Advertisers pay the average CPC of those ads that are ranked below their ads.
C) Advertisers pay only ninety percent of their original CPC rate for every thousand clicks.
D) Advertisers pay one cent more than the minimum needed to retain an ad's position on a page.
E) Advertisers pay the equivalent of the CPC bid by the worst performing ads, taken in a reverse sequence.