Final answer:
A rightward shift in the Aggregate Demand curve on the very flat part of the Aggregate Supply curve will increase real output significantly more than the price level.
Step-by-step explanation:
The question pertains to the effect of a rightward shift in the Aggregate Demand (AD) curve on real output and price levels, specifically when the Aggregate Supply (AS) curve is very flat, which is indicative of the Keynesian range. In this range, capacity is underutilized, and firms can increase production without a significant rise in prices. Therefore, a rightward shift in the AD curve in this range would result in A) an increase in real output by more than the price level. This is because producers can meet the higher demand by increasing production with little to no increase in price levels due to the excess capacity.