Which situation illustrates an increase in demand?

The scenario that accurately illustrates an increase in demand is when there is an increase in the price of substitutes, leading to an increase in demand for the product. When the price of a substitute good rises, consumers are likely to shift their preference to a relatively less expensive alternative. This behavior reflects the law of demand, wherein as the price of a good goes up, demand for that good typically rises if consumers find it to be a more attractive option compared to its substitute.

In this context, the demand curve for the original product shifts to the right, indicating an increase in demand due to the changed relative prices. This captures the essence of how consumer behavior adapts to changes in market conditions, demonstrating the interconnectedness of goods within the market.

The other options do not demonstrate an increase in demand: a decrease in consumer income would generally decrease demand for luxury cars as they are high-priced items; a seasonal sale that leads to decreased consumer interest is indicative of lower demand; and an increase in wages that results in decreased demand for inferior goods shows what happens when people have more income to spend, leading them away from goods typically purchased when income is lower.