Suppose that Jane enjoys Diet Coke so much that she consumes one can every day. Although she enjoys gourmet cheese, she consumes it sporadically. If the price of Diet Coke rises, Jane decreases her consumption by only a very small amount. But if the price of gourmet cheese rises, Jane decreases her consumption by a lot. These examples illustrate the importance of the availability of:__________.
a. close substitutes in determining the price elasticity of demand
b. the time horizon in determining the price elasticity of demand.
c. a necessity versus a luxury in determining the price elasticity of demand.
d. the definition of a market in determining the price elasticity of demand.

Necessity goods are the goods or services that a consumer will continue buying whether income falls or the price rises. This type of goods are considered essential. The are not sensitive to price. To Jane, Diet coke is a necessity because she takes it everyday.

While luxury goods are goods that are really not essential. They are owned or bought for the sake of showing wealth or affluence. To Jane, gourmet cheese is a luxury good.