Answer:
C. when the aggregate expenditure line intersects the 45o line at a level of GDP below potential GDP
Explanation:
When this occurs the economy is in recession, when the line intersects above the potential GDP then, the economy is also en recession.
The economy will enter in recession also, if the level of demanded expenditures excees the level of the level of output. Once the shelves are empied, the business can consider to increase output or prices to met hte demand.