Which of the following statements is CORRECT?

a$.$ If a firm finds that the cost of debt is less than the cost of equity, increasing its debt ratio must reduce its WACC.

b$.$ The capital structure that minimizes the firm's weighted average cost of capital is also the capital structure that maximizes its earnings per share.

c$.$ The capital structure that minimizes a firm's weighted average cost of capital is also the capital structure that maximizes its stock price. just tell me what it means and the logic to find the answer