Consumers have been buying fewer CDs as downloadable music has become easier to purchase and use. We would represent this as

a leftward shift of the demand curve for CDs.

Explanation:

Most economists use the aggregate demand and aggregate supply model primarily to analyze short-run fluctuations in the economy.

This simply means that, whatever makes the factors of production such as, land, labor, entrepreneurship, capital, or efficiency to either go up or down would certainly result in fluctuations in the economy of a particular country.

Aggregate supply (AS) refers to the total quantity of output (goods and services) that firms are willing to produce and sell at a given price in an economy at a particular period of time.

Aggregate demand (AD) can be defined as the total quantity of output (final goods and services) that is demanded by consumers at all possible price levels in an economy at a particular time.

On a standard Aggregate demand (AD)-Aggregate supply (AS) curve, the y axis denotes the Price (P) of goods and services while the x axis typically denotes the Output (Q) of final goods and services.

In the short-run, a rightward shift in the aggregate supply (AS) curve causes output to increase and result in a price fall (lower price) while a rightward shift in the aggregate demand (AD) curve also cause output to increase and rise in prices.

In this scenario, consumers have been buying fewer CDs as downloadable music has become easier to purchase and use. We would represent this as a leftward shift of the demand curve for CDs.