Raymond's preferences are represented by the utility function U(x; y) = x/y if y > 0 and

U(x; y) = 0 if y = 0.

(a) Raymond has indierence curves that are rectangular hyperbolas.

(b) Raymond prefers more of each good to less.

(c) Raymond has quasi-linear preferences.

(d) Raymond has a bliss point.

(e) Raymond has indierence curves that are upward sloping straight lines if y > 0.

这道题为什么选e. y>0时，U(x; y) = 0与无差异曲线还会是向上倾斜的直线？这会不会矛盾？