Which of the following factors would cause a demand curve to shift to the right?

A rightward shift in the demand curve indicates an increase in demand for a product or service at all price levels. The correct choice highlights that an increase in the number of buyers leads to higher demand. When more consumers enter the market, they create greater competition for the existing supply, prompting sellers to increase prices or expand production to meet the new demand levels. This is a basic principle of supply and demand; more buyers translate to greater overall demand, leading to a rightward shift of the demand curve.

The other factors presented would not typically lead to a rightward shift. A decrease in income generally reduces consumers' purchasing power, thus lowering demand for most goods, particularly normal goods. An increase in the prices of related goods can decrease demand for the original good if they are substitutes because consumers may opt for the less expensive substitute. A decrease in consumer tastes negatively affects demand; if consumers prefer other products, they will purchase less of the original item. Hence, the correct answer reflects the fundamental economic relationship where an increase in the number of buyers enhances total demand.