Which of the following statements is true? Select one: a. The duration of equity is equal to the duration of assets minus the duration of liabilities. b. Duration gap measures the impact of changes in interest rates on the market value of equity. c. The optimal duration gap is zero. d. The shorter the maturity of the FI's securities, the greater the FI's interest rate risk exposure. e. The duration of all floating rate debt instruments is equal to the time to maturity.