• The correct answer is C. trough.

The business cycle has four main stages. The first one is an expansion that is characterized by steady economic growth. The second stage is the peak, which is the maximum economic growth achieved by the country. The third stage is the recession that is distinguished by a decline in the real GDP. Finally, the fourth stage is a trough, which is the lowest point of the business cycle. Therefore, the correct answer is option C.

On the contrary, option A. is incorrect because a recession is a stage lived by an economy prior to the lowest point. Option B. is also incorrect because an economic downturn is only a decline in the economic activity of the country. Option D. is incorrect because the term "base" is not associated with the business cycle.