Which of the following statements regarding cost of capital and firm value is true? A. At minimal capital structure, a firm's cost of capital is minimized, and its total value is maximized. B. At optimal capital structure, a firm's cost of capital is maximized, and its total value is maximized. C. At maximum capital structure, a firm's cost of capital is optimized, and its total value is maximized. D. At optimal capital structure, a firm's cost of capital is minimized, and its total value is maximized