Tri-State Electric is a profitable utility company that has increased its dividend to common stockholders every year for 42 consecutive years. Which of the following is least likely to affect the market price of the company's preferred stock by a significant amount?

a. A decrease in long-term interest rates.

b. An increase in long-term interest rates.

c. The board of directors announces its intention to increase common stock dividends in the current year.

d. Whether or not the preferred stock carries a conversion privilege.