This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Functional residual capacity of lung is defined as 
Select and explain. 
A. Volume expired after normal expiration, B. Volume remaining after forced expiration, C. ERV + RV, D. Tidal volume + volume inspired forcefully
C: ERV + RV
Answer: C: ERV + RV 
Explanation: The amount of air that remains in lung after a normal expiration.