Final answer:
Macroeconomics studies the short-run variations in economic growth, known as business cycles, which are the periods of macroeconomic expansion and contraction around a long-term trend, marked by changes in GDP growth rates. option a is answer
Step-by-step explanation:
Macroeconomics deals with the short-run variations in economic growth that make up the business cycles. A business cycle represents a period of macroeconomic expansion followed by a period of contraction. These are also known by economists as market fluctuations.
They occur around a long-term growth trend and usually involve shifts between periods of rapid economic growth and periods of stagnation or decline. The growth rate of real gross domestic product often measures these fluctuations.
The economy does not always grow at its average growth rate; it cycles around the long-run trend. We can see this in various phases of the business cycle where sometimes economic activity grows at, above, or below the trend, and can even experience a decline.
The economic history of the United States is cyclical with recessions and expansions, such as the downturn during the Great Depression. The aggregate demand-aggregate supply model helps us understand the causes of these cycles and why the economy grows at different rates during different years. option a is answer