21. What utility function does NOT represent the preferences of an individual over soda [5] and ice [I], where the individual onlv en|ovs Ice-cold glasses of soda {or fractions of ioe-oold glasses of soda]. To make a proper loe-cold glass at soda, the soda and ice must he in a 1:3 ratio. For instance, 1.5 sodas and 4.5 ice ashes would make 1.5 glasses of ice-oold soda. A. U(S,I} =min{3s,1} a. U(S,I}=min{3,%} c; U(S,I}=(min(l.53,%))2 D. AC are all valid representations E. AC contains no valid representations