Which of the following is true about price discrimination? a. when there are a number of competing firms, price discrimination is less likely because competitors tend to undercut the high prices charged those discriminated against. b. a profit-maximizing seller will charge a higher price for those with a greater willingness to pay, and a lower price for demanders with a lower willingness to pay. c. price differentials between groups will erode if reselling is easy. d. quantity discounts are a form of price discrimination which allow a seller to charge a higher price for the first unit than for later units. e. all of the above are true of price discrimination.