Concept:The law of demand may fail for commodities whose demand rises with price.
Explanation:The law of demand states that as price increases, quantity demanded falls.
This holds for normal and conventional goods.
But rare commodities, such as antiques or precious collectibles, behave differently.
For rare items, a higher price may increase their prestige and perceived value.
As a result, consumers may demand more of them at higher prices.
Therefore, the law of demand will not hold when rare commodities are involved.
Answer:C. rare commodities are involved.