The correct option is
C Fraudulent collusion between bidders
A cartel is an organization created from a formal agreement between a group of producers of a good or service to regulate supply in an effort to regulate or manipulate prices. In other words, a cartel is a collection of otherwise independent businesses or countries that act together as if they were a single producer and thus are able to fix prices for the goods they produce and the services they render without competition.
A cartel is a group of apparently independent producers whose goal is to increase their collective profits by means of price fixing, limiting supply, or other restrictive practices. Cartels typically control selling prices, but some are organized to control the prices of purchased inputs. Antitrust laws attempt to deter or forbid cartels. A single entity that holds a monopoly by this definition cannot be a cartel, though it may be guilty of abusing said monopoly in other ways. Cartels usually occur in oligopolies, where there are a small number of sellers and usually involve homogeneous products.