please all 4 tests

3) A cartel is defined to be A) any oligopolistic industry with fewer than 4 firms. B) a form of oligopoly in which firms agree to sell at different prices like in monopolistic competition. C) a form of oligopoly in which firms formally agree to establish a common strategy, often a common price, in effect acting like a monopoly, D) a form of oligopoly in which firms agree to compete with each other on an equal basis. 4) Prices under an ideal cartel situation will be equal to A) monopoly prices. B) competitive prices. C) prices under monopolistic competition. D) marginal cost. 5) Third-degree price discrimination exists when A) the seller knows exactly how much each potential customer is willing to pay and will charge accordingly. B) different prices are charged by blocks of services. c) when the seller can separate markets by geography, income, age, etc., and charge different prices to these different groups. D) when the seller will bargain with buyers in each of the markets to obtain the best possible price. 6) Revenue maximization occurs when a firm sells at a price A) that is equal to its minimum average variable cost. B) where its marginal revenue is equal to its marginal cost. C) where its marginal revenue is zero. D) None of the above