The correct answer is C. Law of diminishing marginal utility.
The law of diminishing marginal utility states that as a person consumes more of a good or service, the additional satisfaction or benefit they receive from each additional unit decreases. In other words, the first glass of lemonade will give the thirsty boy the most satisfaction, the second glass will give him less satisfaction, and so on.
The law of diminishing marginal utility is a fundamental principle of economics that helps to explain why people make the choices they do. It is also used to explain why prices tend to fall as more of a good or service is produced.
The law of diminishing marginal utility can be applied to many different goods and services. For example, if you are hungry, the first bite of food will give you the most satisfaction. The second bite will give you less satisfaction, and so on. Similarly, if you are thirsty, the first glass of water will give you the most satisfaction. The second glass will give you less satisfaction, and so on.
The law of diminishing marginal utility is a powerful tool that can be used to understand human behavior. It is a fundamental principle of economics that helps to explain why people make the choices they do.