Concept:Marginal utility is the change in total utility from consuming one extra unit.
Explanation:When marginal utility is positive, total utility rises.
When marginal utility is zero, total utility is at its maximum.
When marginal utility is negative, total utility falls.
Thus, a falling total utility implies that marginal utility is negative.
Out of the given relationships, this matching is correct.
Answer:B. falling, marginal utility is negative.