The correct answer is: B. varies inversely with price.
A demand schedule is a table that shows the relationship between the price of a good and the quantity of that good that consumers are willing and able to purchase at that price. The law of demand states that, all other things being equal, the quantity demanded of a good will decrease as the price of that good increases. This is because consumers are generally willing to purchase more of a good when the price is lower.
Option A is incorrect because quantity demanded does not vary directly with price. In fact, quantity demanded varies inversely with price.
Option C is incorrect because quantity demanded does not vary proportionately with price. The law of demand states that the quantity demanded of a good will decrease as the price of that good increases, but it does not state that the quantity demanded will decrease by a certain percentage for every percentage increase in price.
Option D is incorrect because the law of demand is a well-established economic principle that has been supported by empirical evidence.