Which of the Following Correctly Identifies the Trade-Off That a Budget

Which of the following correctly identifies the trade-off that a budget constraint represents?

A) The amount of income that must be given up to obtain an additional unit of a good
B) The maximum amount of two goods that a consumer can purchase given his income
C) The optimum combination of goods that a consumer with a given income should purchase
D) The amount of one good that has to be given up to purchase an additional unit of the other good