Which of the following directly leads to a shift in the demand curve?

A change in consumer preferences is a direct factor that leads to a shift in the demand curve. When consumer tastes and preferences evolve, it can significantly affect the quantity of a good or service demanded at a given price. For example, if a popular health trend promotes the consumption of organic foods, more consumers may choose to buy these products, resulting in an increase in demand. This change moves the demand curve to the right. Conversely, if a product falls out of favor, the demand may decrease, shifting the curve to the left.

Other factors listed, such as changes in production technology, the number of suppliers, or fixed costs, primarily impact the supply side of the market rather than directly shifting the demand curve. These factors can influence the overall market dynamics and pricing but do not specifically change consumer preferences or the willingness to purchase a good or service at various price levels.