Which of the following statements about different tax rates over time is false? a) A 5% increase in the tax rate for year 4 has less effect on NPV than a 5% increase in the tax rate for year 10. b) A 5% increase in the tax rate for year 10 has less effect on NPV than a 5% increase in the tax rate for year 4. c) Future tax rates used in NPV calculations are estimates because Congress can change tax rates. d) A firm's future tax rate may change because of increases or decreases in future taxable income.