The long-run aggregate supply curve would shift left if the amount of labor available

a. decreased or Congress made a substantial increase in the minimum wage.

b. increased or Congress made a substantial increase in the minimum wage.

c. decreased or Congress abolished the minimum wage.

d. increased or Congress abolished the minimum wage.

The correct answer is option a.

Explanation:

The long run aggregate supply curve is inelastic and vertical in shape. The reason behind this is that in the long run the output level is not affected by the change in price level. It is rather affected by the quantity of inputs.

A leftward shift in the long run aggregate supply means that the output level is decreasing. This decrease in input in this case is either because of decrease in quantity of labor available, or because of increase in minimum wages the firms are hiring less labor.

So, option a is the correct answer.