Please use the CAPM logic to choose which if any of the following statements is (are) true. Explain.

a) The cost of equity is higher than the cost of debt for all firms.

b) The cost of equity is higher than the cost of debt only for firms whose debt is risk-free.

c) The cost of equity is higher than the cost of debt only if the firms beta is positive.

d) The cost of equity is higher than the cost of debt only if the firms beta is positive and when its debt is risk free.