Which of the following statements is true?
A. The longer any price change persists, the greater the elasticity of demand.
B. The closer the substitutes for a particular commodity and the more substitutes there are, the more inelastic will be its price elasticity of demand.
C. The smaller the share of a person's total budget that is spent on a commodity, the greater that person's price elasticity of demand is for that commodity.
D. The demand for necessities is likely to be elastic, while the demand for luxuries is likely to be inelastic.