What do the income effect, the substitution effect, and diminishing marginal utility have in common?

A) All are required to explain the utility-maximizing position of a consumer.
B) They are all empirically measurable.
C) They all help explain the upsloping supply curve.
D) They all help explain the downsloping demand curve.

These concepts all contribute to explaining why demand curves typically slope downwards, indicating that as the price of a product decreases, consumers are more likely to purchase more of it. The income effect suggests that a lower price increases the purchasing power of consumers, allowing them to buy more. The substitution effect indicates that as the price of a product decreases, it becomes relatively cheaper compared to substitutes, leading consumers to switch their purchases to the cheaper option. Diminishing marginal utility explains that the more of a good consumers have, the less additional utility (satisfaction) they get from consuming more, which influences how much they're willing to pay for additional units, contributing to a downward-sloping demand curve.