For each of the following pairs of investments, indicate which would always be preferred by a rational investor (assuming that these are the only investments available to the investor): a. Portfolio A Portfolio B Preference b. Portfolio C Portfolio D Preference: c. Portfolio E Portfolio F Preference: r = 16% r = 12% O Portfolio A O Portfolio B O Indeterminate r = 21% r = 19% O Portfolio C O Portfolio D O Indeterminate r = 12% r = 12% O Portfolio E O Portfolio F O Indeterminate 0 = 18% 0 = 18% o = 0 = 24% 18% 0 = 18% o = 12%