The short-run aggregate supply curve shows: O Changes in output in an economy as the price level changes, holding all other determinants of real GDP constant What happens to output in an economy when the government spends more money The relationship between the price level and aggregate expenditure How firms respond to changes in interest rates Which of the following are assumed to remain unchanged along a given short-run aggregate supply curve? 1. Institutions, such as patent laws and tax systems, that make up the "rules of the game 2. The position of the aggregate demand curve 3. Input prices 4. Real GDP