Shana's behavior of continuing to buy a necessary medicine despite a sharp increase in its price shows that the demand for necessities is inelastic. Inelastic demand means that consumers will continue to purchase a good or service even if the price rises significantly, because it is essential and has few or no substitutes. This contrasts with goods that have elastic demand, where a price increase would lead to a significant decrease in quantity demanded. Shana's case illustrates that necessary medicines are typically goods with inelastic demand.