Answer:
D) Marginal utility of the last unit of each product consumed is the same.
Explanation:
To maximize utility with a given income constraint, a consumer must chose products to maximize utility. This can be done so that each extra dollar, which is the marginal income, spent on each of these products yields the equal marginal utility. For example if one product yields more marginal utility per marginal dollar spent, the consumer should reallocate their income so they consume more of this product and less of others, so much so that the utility derived from this product equals utility derived from other products.
Utility is maximized when these marginal utilities per marginal dollar spent coincide.
Hope that helps.