A movement along the short-run AS curve occurs, holding everything else constant, when there is a:

a. change in the aggregate price level.
b. productivity change.
c. supply shock.
d. change in commodity prices.

The answer is A)change in the aggregate price level.

Explanation:

A supply curve is a graphical illustration of the relationship between the amount of a commodity that a producer or supplier is willing to offer with respect to the price of goods at any given time.  

It is the graphical representation of a supply schedule.

In a graph, the price of the commodity is shown on the vertical axis and the quantity supplied is shown on the horizontal axis.  

The higher the price, the higher the quantity supplied, the lower the price, lesser will be the quantity supplied and can e represented as movements in a supply curve.

The movement in supply curve can be an extension or contraction.  

Extension in a supply curve is caused when there is an increase in the price or quantity supplied of the commodity while contraction is caused due to a decrease in the price or quantity supplied of the commodity.

A movement along the short-run AS curve occurs, holding everything else constant, when there is a change in the aggregate price level.

answer; 20% is your answer;

reducing the scale of the market for a new product.