For an airline, the price of economy-class seats on any given flight may fluctuate over time. For example, the airline may try to fill economy-class seats by lowering the price as the day of the flight draws closer, or try to fill business-class seats first by raising prices on economy tickets. This is an example of: 
 a. market pricing. 
 b. price skimming 
 c. odd pricing 
 d. dynamic pricing. 
 e. seasonal discounts