In a return-standard deviation space, which of the following statements is (are) true for risk-averse investors? (The vertical and horizontal lines are referred to as the expected return-axis and the standard deviation-axis, respectively.) I) An investor's own indifference curves might intersect; II) Indifference curves have negative slopes; III) In a set of indifference curves, the highest offers the greatest utility; IV) Indifference curves of two investors might intersect.