Final answer:
Following a trough in the business cycle, real GDP increases, as the economy begins to recover and enter into the expansion phase.
Step-by-step explanation:
The question is regarding the phases of the business cycle and how they relate to changes in real GDP. Specifically, it asks what happens to real GDP following a trough. Based on the business cycle, which consists of periods of expansion and contraction, the correct answer is that following a trough, real GDP increases. During a recession, real GDP declines, and this period starts at the peak and ends at the trough. After the trough, the economy typically begins to recover, and as a result, real GDP starts to increase again.
Therefore, the correct answer is: Following a trough, real GDP increases. That corresponds to option C. This is because a trough represents the lowest point of the business cycle, after which the expansion phase begins, leading to an increase in economic activity and real GDP.