In the Context of Purchasing Advertising Space,some Publishers Charge Their

In the context of purchasing advertising space,some publishers charge their clients according to click-throughs,that is:

A) the clients need to pay when a user actually clicks on a banner ad to visit the advertiser's landing page.
B) the clients need to pay when a user clicks to visit the Web site on which the ad is displayed.
C) the clients need to pay only when a consumer purchases a product from the advertiser's home page.
D) the clients need to pay in advance for uploading their ads on a Web site.
E) the clients need to pay a fixed amount for every banner ad.