Suppose That the Market Demand and Supply Curves for Granola

Multiple Choice

Suppose that the market demand and supply curves for granola bars are represented by the equations:
Q^D = 7,000 - 120P
Q^S = -50 + 20P
Where Q^D is the quantity demanded, Q^S is the quantity supplied, and P is the price. Which of the following is true for these market demand and supply curves?

A) The law of demand holds because the derivative of the demand with respect to price is -120.
B) The law of demand holds because the derivative of the demand with respect to price is 20.
C) The law of demand does not hold because the derivative of the demand with respect to price is -120.
D) The law of demand does not hold because the derivative of the demand with respect to price is 20.