In the real world, demand curves are probably not linear, but we use linear demand curves in our model because

a.The Law of Demand does not always hold in the real world and using linear demand curves makes sure the Law of Demand holds in our model.

b.Linear demand curves better represent consumer behavior than real world data do.

c.They simplify the model greatly while still allowing us to make good qualitative predictions.

d.It is mathematically impossible to derive real world demand curves.