The determinants of aggregate demand: A. explain why the aggregate demand curve is downsloping. B. explain shifts in the aggregate demand curve. C. demonstrate why real output and the price level are inversely related. D. include input prices and resource productivity.

Letter b is correct!

explanation:

The letter b is correct because it is the demand determinants that explain the changes in the aggregate demand curve. This is because the most important determinants of demand such as interest rate, Federal Deficit, expectations and money supply are not constant, so a change in any of these determinants will also affect the change in the aggregate demand curve.