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 r=17% r=13% =19% Portfolio B =19% Portfolio A Preference Portfolio B Indeterminate b. Portfolio C r=18%r=16%=19%=13% Portfolio C Preference: Portfolio D Indeterminate c. Portfolio E r=9%r=9%=13%=7% Portfolio E Preference: Portfolio F Indeterminate