Concept:The law of diminishing marginal utility states that as a consumer continues to consume more units of a commodity, the extra satisfaction gained from each additional unit tends to decrease.
Explanation:When a consumer increases consumption continuously, each successive unit gives less additional utility than the previous one.
This means that marginal utility, which is the satisfaction from the last unit consumed, must fall as consumption rises.
Total utility, however, may still be rising during this process, but it rises at a decreasing rate.
Option A is incorrect because total utility does not necessarily fall; it may continue rising.
Option C is wrong because the law states a definite fall, not a possible rise.
Option D describes a situation that can occur, but the law specifically indicates that marginal utility must fall as consumption increases continuously.
Answer:B. marginal utility must fall