What does the demand curve illustrate?

The demand curve illustrates the quantity of a product demanded at different prices, demonstrating the fundamental economic principle of how price levels influence consumer behavior. As the price of a good decreases, the quantity demanded typically increases, and vice versa; this relationship is graphically represented by a downward sloping curve.

Understanding the demand curve is essential for analyzing market dynamics, as it helps businesses and marketers set prices based on consumer willingness to purchase at various price points. This visual representation goes beyond just numeric data, allowing for clearer insights into consumer preferences and market demands.

In contrast, the other options focus on different aspects of economics. One pertains to production costs and does not directly relate to consumer demand; another discusses the relationship between costs rather than how prices affect demand; while the last one involves income changes which can shift the entire demand curve rather than illustrate the demand at given price points. Thus, option B is the most accurate in representing the demand curve's purpose in marketing and economics.