Final answer:
If unemployment equals the natural unemployment rate, (A) there is only frictional or structural unemployment, not zero unemployment. This rate includes the typical job search and skills mismatch unemployment, but not the cyclical unemployment related to economic downturns.
Step-by-step explanation:
If unemployment equals the natural unemployment rate, then there is only frictional or structural unemployment. This is because the natural unemployment rate includes the unemployment that persists due to the job searching process (frictional unemployment) and the mismatch between the skills workers have and the skills needed for available jobs (structural unemployment). Cyclical unemployment, on the other hand, occurs due to downturns in the business cycle and is not present when the economy is producing at potential GDP. In this scenario, there would be no cyclical unemployment because we are assuming the economy is performing optimally, at its potential GDP.
When the economy is operating at the natural rate of unemployment, it does not mean there is zero unemployment. Rather, it signifies that the level of unemployment is what would be expected given the economic, social, and political forces in the economy. It also does not imply that there are no job openings; in fact, there could be many job vacancies, as there will always be some degree of job turnover and creation, leading to frictional unemployment.