An elastic products prices are responsive to changes in demand. Generally, the necessity of the product is related to it's elasticity. For example, insulin is essential for diabetics, so the price is extremely inelastic—people will pay any amount because it is a life or death situation. The price of a new MP3 player can be inelastic, especially because results show that people want the newest thing, and will pay more if it works better than the previous model. Additionally, the price of "scalper" tickers to the World Series will increase by demand, but they will still sell regardless. The price of dairy products, however, is rather elastic; this is because when the price rises, people switch to a cheaper brand. The difference between an inelastic and elastic product is that elastic products have substitutes, whereas inelastic products have no substitutes (or sometimes very few).
Answer: A. the price of dairy products
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