Answer:
B. A decrease in short-run aggregate supply.
Step-by-step explanation:
In the case when there is a decrease in the level of the equilibrium price and also in the real GDP so this would result in decrease in aggregate supply i.e. short run
But when there is a decrease in the level of equilibrium price but the real GDP would increase so there is an increase in aggregate supply i.e. short run
So according to the given situation, the option b is ocrrect