Final answer:
In the long run, the economy's output level will stay the same if the price level decreases. Therefore, the correct option is D.
Step-by-step explanation:
In the long run, if the price level decreases, the economy's output level will stay the same.
From a neoclassical perspective, changes in the price level do not have a direct impact on output in the long run. In the long run, potential GDP and aggregate supply determine the size of the economy's output. When prices decrease, there may be a temporary increase in output in the short run as employers can hold down on pay increases or replace higher-paid workers with lower-wage ones, but over time, the output level will return to the potential GDP. Therefore, the correct answer is d. stay the same.