Which of the following is a true statement? A.) To estimate the before-tax cost of debt, we need to solve for the Yield to Maturity (YTM) on the firm's existing debt. B.) To estimate the before-tax cost of debt, we need to solve for the Yield to Call (YTC) on the firm's existing debt. C.) To estimate the before-tax cost of debt, we use the coupon rate of the firm's existing debt. D.) To estimate the before-tax cost of debt, we use the average rate on the firm's existing debt