Select the correct answer. The market demand for milk in Country X is 18 billion gallons per month, but the supply is 10 billion gallons per month. What must happen in order to achieve market equilibrium?
A. The monthly supply of milk must increase by 28 billion gallons.
B. The monthly supply of milk must decrease by 8 billion gallons.
C. The monthly supply of milk must decrease by 28 billion gallons.
D. The monthly supply of milk must increase by 8 billion gallons.