The law of diminishing marginal utility is best expressed as: a) The more a person consumes a product, the smaller the utility that he receives from its consumption. This means that as a person continues to consume more of a good or service, the satisfaction or utility gained from each additional unit tends to decrease.
To elaborate, when you first enjoy a slice of pizza, the satisfaction you get is high. However, as you eat more slices, the enjoyment of each new slice tends to diminish. This principle applies to most goods and services, highlighting that consumption is not linear in terms of satisfaction.