Which statement is true?

Select one:

a. An increase in the market value of preferred stock will increase a firm's weighted average cost of capital.

b. The cost of preferred stock is unaffected by the issuer's tax rate.

c. Preferred stock is generally the cheapest source of capital for a firm.

d. The cost of preferred stock remains constant from year to year.

e. Preferred stock is valued using the capital asset pricing model.