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 (the additional satisfaction or benefit they receive from consuming one more unit of the good) decreases. This is because the consumer’s needs for the good are being met more and more, and they are getting less and less satisfaction from each additional unit.
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 get the same amount of satisfaction from each additional unit of each good they consume.
The law of proportions states that in order to maximize their utility, consumers will consume goods in the proportions that reflect the relative prices of the goods. This means that if the price of one good goes up, the consumer will consume less of that good and more of other goods.
All of these laws are important in 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 consume goods in such a way that the marginal utility of each good is equal. And the law of proportions explains why consumers will consume goods in the proportions that reflect the relative prices of the goods.
Together, these laws help us to understand how consumers make decisions about what goods to consume and how much to consume of each good. They also help us to understand the concept of consumer surplus.