Which of the following statements is CORRECT?

a. Since debt is cheaper than equity, increasing a company's debt ratio will always reduce its WACC.

b. Since debt financing raises the firm's financial risk, increasing a company's debt ratio will always increase its WACC.

c. When a company increases its debt ratio, the costs of equity and debt both increase. Therefore, the WACC must also increase.

d. The capital structure that maximizes the stock price is generally the capital structure that also maximizes earnings per share.

e. All else equal, an increase in the corporate tax rate would tend to encourage a company to increase its debt ratio.