Final answer:
The correct way to read a demand curve is 'over and down', making option A (3 only) the true statement for how to interpret a demand curve in the context of price and quantity demanded.
Step-by-step explanation:
The correct answer to which statements are true about how to read a demand curve and a marginal benefit curve is option A: 3 only. Demand curves are typically read from left to right; as you move rightward (over) along the curve, you go downward (down) to see the decrease in price that corresponds with an increase in quantity demanded. This is a reflection of the law of demand, which states that, ceteris paribus, as the price of a product falls, the quantity demanded will increase and vice versa.
In contrast, a marginal benefit curve, which can also represent a demand curve, reflects the maximum price consumers are willing to pay for each additional unit. As you consider additional units, moving rightward over the curve, you also move downward to indicate a decrease in willingness to pay for subsequent units.
From the given information, it's clear that we do not typically read a demand curve or a marginal benefit curve 'up and over' as options 1 and 2 suggest, making these statements incorrect and further confirming that option A (3 only) is the correct choice.