Which of the following best explains why prices tend to be inflexible even when demand changes?
a. Government regulations limit the number of times a firm can change prices in a year.
b. In most industries the profit-maximizing price does not change even when demand changes.
c. Production costs do not tend to change when a firm varies its level of output.
d. Firms may be reluctant to change prices for fear of setting off a price war or losing customers to rivals.