To determine the correct answer regarding the natural rate of output at the points Y1, Y2, Y3, we typically need to reference the characteristics of the long-run aggregate supply (LRAS) and the potential output in a typical aggregate demand and supply graph.
The natural rate of output is often represented where the aggregate supply curve intersects the aggregate demand curve in the long run, typically aligned with the potential output level.
If the figure indicates that Y1 is associated with the long-run aggregate supply, that would suggest that option b. Y1 is correct. However, without the figure itself or additional context, it's not possible to definitively choose.
If you have access to the figure or can describe it, I can provide a more precise answer.