What exemplifies a change in product price due to a drop in quantity demanded?

The situation described in the correct choice illustrates a change in product price as a direct response to a decrease in quantity demanded. In this case, the grocery store marks down the price of unsold candy after Valentine's Day. The unsold inventory indicates that the demand for this particular candy has dropped significantly after the holiday, where it was likely more popular. By lowering the price, the grocery store attempts to entice customers to purchase these items, thereby addressing the decline in demand and clearing inventory.

This approach highlights the concept that when demand for a product decreases, sellers may reduce prices to stimulate interest and boost sales. The other options reflect varying scenarios of price adjustments but do not directly address a drop in quantity demanded as the primary factor for the price change. In the other choices, the price changes are driven by different motivations such as raising prices due to popularity, stimulating sales with discounts, or seasonal marketing strategies, rather than responding to a decrease in demand for a specific product.