A sentence has been given in Direct/Indirect Speech. Out of the four given alternatives, select the one which best expresses the same sentencein Indirect/Direct Speech.
The long-run aggregate supply curve is vertical because it is at the full-employment or potential output. Because the economy's potential output is determined by the availability and productivity of real resources, not by the price level. That means that even if demand increases, firms can't hire new workers and expand because everyone is already working.