Final answer:
The price of roses is expected to decrease the day after Valentine's Day due to a leftward shift in the demand curve, indicating a lower quantity demanded at every given price.
Step-by-step explanation:
The student's question involves understanding how the demand curve affects the price of a product after a notable change in demand. Specifically, the day after Valentine's Day, the price of roses can be expected to go down; this occurs because the demand curve shifts to the left. The rightwards shift in the demand curve signifies an increase in demand at every price level, while the leftwards shift indicates a decrease in demand. Since Valentine's Day increases the demand for roses, the subsequent day would naturally see a diminished demand, leading to a leftward shift in the demand curve and a decrease in price.