Which of the following is not definitely true for a firm which currently has a negative net debt to equity ratio in its capital structure?

a. The firm is not at its optimal capital structure based on trade-off theory b. Company cost of capital can be decreased by adding debt to the capital structure c. Earnings would increase if debt is added to the capital structure d. Firm value can be increased by adding debt to the capital structure e. The firm has more cash or cash equivalents than debt