Answer: Decrease, Increase, Price flexibility.
Explanation: According to classical economics, a decrease in aggregate demand causes the price level to DECREASE in the long run. On the other hand, an increase in aggregate demand causes the price level to INCREASE in the long run. These changes occur because of PRICE FLEXIBILITY.
In a flexible market the forces of demand and supply determines the prices of commodities in the market.
As the demand Falls the prices also fall as the demand rises the prices of commodities also rises.