Which of the following statements is CORRECT?

a$.$ All else equal, an increase in the corporate tax rate would tend to encourage companies to increase their debt ratios.

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

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

d$.$ Since the cost of debt is generally fixed, increasing the debt ratio tends to stabilize net income.

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