The correct answer is: D. small change in price causes big changes in demand.
Demand is elastic when a small change in price causes a big change in demand. This means that consumers are very sensitive to changes in price, and will buy more or less of a good depending on how much it costs.
Option A is incorrect because it describes inelastic demand. Inelastic demand is when a change in price does not cause a big change in demand. This means that consumers are not very sensitive to changes in price, and will continue to buy the same amount of a good even if the price goes up or down.
Option B is incorrect because it describes a change in fashion, not a change in price. A change in fashion can cause a change in demand, but it does not necessarily mean that demand will be elastic.
Option C is incorrect because it describes a change in income, not a change in price. A change in income can cause a change in demand, but it does not necessarily mean that demand will be elastic.