Final answer:
The changes in prices of other products affecting the demand for an item are known as cross-elasticity of demand, which can be positive for substitute goods and negative for complementary goods.
Step-by-step explanation:
The phenomenon where the changes in prices of other products affect the demand for an item is called cross-elasticity of demand. This economic concept is important when considering how the market for one good is interconnected with the market for another.
For example, when two goods are substitutes, like coffee and tea, an increase in the price of tea can lead to an increased demand for coffee, indicating a positive cross-price elasticity of demand. Conversely, for complementary goods like coffee and sugar,
an increase in the price of sugar would typically result in a decreased demand for coffee, showing a negative cross-price elasticity. Therefore, the correct answer to the student's question is A) cross-elasticity of demand.