A pyramid scheme is a type of business structure that is commonly associated with a style called (D) multi-level marketing.
Multi-level marketing relies a lot on the acquisition of new distributors to sell the products, since these people would be the one who will generate the revenue needed for the business that uses this model. It is a controversial business practice since often times, the one who is at the very bottom of the level would end up exploited by the one at the top, since they usually have to pay to get the products they sell.