Recently, Lisa's wealth increased by $500. If her wealth were to increase by another $500 in the near future, then her utility would increase, but not by as much as it increased with the recent increase to her wealth. Based on this information, and graphing wealth on each horizontal axis, Lisa's utility function a. is downward sloping and her marginal utility function is upward sloping. b. and marginal utility function are both downward sloping. c. and marginal utility function are both upward sloping. d. is upward sloping and her marginal utility function is downward sloping