Which of the following would be most likely to lead to a decrease in a firm's dividend payout ratio?

a. Its accounts receivable decrease due to a change in its credit policy.

b. Its stock price has increased over the last year by a greater percentage than the increase in the broad stock market averages.

c. Its access to the capital markets increases.

d. Its R&D efforts pay off, and it now has more high-return investment opportunities.

e. Its earnings become more stable.