Daniel Zimiles will buy more and more baseball cards until

A) the total utility of cards begins to fall.
B) the total utility of the cards falls to zero.
C) the marginal utility of the cards starts to fall.
D) the marginal utility of the cards falls to the price of the cards.
E) the marginal utility of the cards falls to zero.

Daniel Zimiles will continue to buy more baseball cards until the marginal utility of the cards falls to the price of the cards. This is because consumers maximize their utility when the last dollar spent on each good provides the same level of satisfaction, which occurs when the marginal utility of a good equals its price.