Final answer:
The correct statement is that the service sector comprises approximately three quarters of the United States' economy and employment.
Step-by-step explanation:
The correct statement is a. The service sector comprises approximately three quarters of the United States' economy and employment.
The service sector, also known as the tertiary sector, encompasses various industries that provide services rather than physical products. Jobs in the service sector include engineering, finance, restaurants, sports, childcare, and medicine. According to data from the US Bureau of Economic Analysis, the service sector makes up more than three quarters of the US economy, as measured by its share of the gross domestic product (GDP).
By contrast, traditional smokestack industries, which refer to manufacturing industries, have not increased in importance in recent years. Rather, the growth and prominence of the service sector have shaped the US economy and employment landscape.