Which of the following statements is true?
a. Firms that can identify two types of consumers can price-discriminate perfectly.
b. Firms can price-discriminate only if there is zero competition in the market.
c. Firms that price-discriminate will not reach higher profits.
d. Firms that can prevent reselling can engage in price discrimination.
e. Firms can usually price-discriminate if they are in a perfectly competitive market.