The WACC is computed as the weighted average of the cost of equity and the cost of debt. Which of these is correct? The cost of debt is:

a. the coupon rate of the firm's recently issued bond, if the bond was issued at a discount.

b. the coupon rate on the firm's recently issued bond, if the bond was issued as a premium.

c. the coupon rate of the firm's recently issued bond, if the bond was issued at par.

d. the cost of debt is never the coupon rate.