Final answer:
The correct answer is (a) the law of demand. This economic principle states that consumers will purchase more of a good or service at lower prices than at higher prices, assuming all other factors stay the same.
Step-by-step explanation:
The statement refers to the law of demand, which is a fundamental concept in economics. This law posits that, given all other factors are held constant, the quantity demanded of a good or service will be inversely related to its price. In simpler terms, this means that consumers will buy more of an item at a lower price than they would at a higher price. The concept of the law of demand is critically important in understanding market economies and consumer behavior.