The correct answer is: D. All of the above
Consumer surplus is the difference between the maximum amount a consumer is willing and able to pay for a good and the price they actually pay. It is a measure of the benefit that consumers receive from consuming a good.
The law of diminishing marginal utility states that as a consumer consumes more of a good, the marginal utility (additional satisfaction) they receive from each additional unit of consumption decreases. This is because the consumer’s needs for the good are being met more and more, so each additional unit of consumption provides less and less satisfaction.
The law of equi-marginal utility states that a consumer will maximize their utility by consuming goods in such a way that the marginal utility of each good is equal. This means that the consumer will consume goods until the marginal utility of each good is equal to the price of the good.
The law of proportions states that in order to maximize utility, a consumer should allocate their income in such a way that the marginal utility of each good is in proportion to its price. This means that the consumer should spend more on goods that have a higher marginal utility and less on goods that have a lower marginal utility.
All of these laws are important for understanding consumer surplus. The law of diminishing marginal utility explains why consumers are willing to pay more for the first unit of a good than they are for the second unit, and so on. The law of equi-marginal utility explains why consumers will only consume goods until the marginal utility of each good is equal to the price of the good. And the law of proportions explains how consumers should allocate their income in order to maximize utility.
Together, these laws explain why consumers are willing to pay more for a good than the price they actually pay, and this difference is known as consumer surplus.