Answer:
The correct answer is: decrease in demand.
Step-by-step explanation:
The equilibrium price and quantity are determined through the intersection of demand and supply curves.
An increase in demand will cause the demand curve to move to the right. This will cause both the price level as well as quantity to increase.
A decrease in supply will cause the supply curve to shift to the left. This will cause the price to increase and quantity to decline.
A decrease in the demand curve will cause the demand curve to shift to the left. This will cause the price as well as quantity to decline.