Final answer:
The law of demand is best completed with option B, which states that the higher the price of a good, the smaller the quantity demanded; and vice versa, demonstrating the inverse relationship between price and quantity demanded.
Step-by-step explanation:
The law of demand states that other things remaining the same, the higher the price of a good, the smaller is the quantity demanded; and the lower the price of a good, the greater is the quantity demanded. Thus, the correct completion for the statement is option B. Demonstrating this with an example, if the price of a pencil is $1, and at this price, consumers buy 100 pencils, but if the price rises to $2 and other factors remain unchanged, the quantity demanded might drop to 50 pencils. Conversely, if the price decreases to $0.50, the quantity demanded might increase to 150 pencils, illustrating the inverse relationship between price and quantity demanded as per the law of demand.