A change or shift of a demand curve occurs when the other factors, other than the price, such as the income changes, happens. Any change that increases the quantity that buyers wish to buy at a given price causes a shift of the demand curve to the right. Buying high fashion brands, eating out in luxury restaurants, preferring air travel instead of bus travel, or going to a cinema instead of watching a movie at home are mostly interrelated with the price of the service/product and the income of the individual. However, when the situation related with the Valentine’s day is taken into account, it can be seen that the cause of the increase of the sales is related with it’s being a special day rather that the increase of the incomes of the customers or the price cut of the flowers. The correct answer is Choice C.