Which statement is correct?

a. At the far right, the aggregate supply curve becomes nearly vertical.
b. The prices for not influence firms' decisions about what quantity to supply.
c. The aggregate supply curve shows how producers as a group will respond to a decrease in aggregate demand.
d. When the economy is at the far left of the aggregate supply curve, a relatively small increase in the prices of outputs that businesses sell, assuming there is no rise in input prices, encourages a slight surge in the quantity of aggregate supply.