This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Physiology
In the expiratory flow volume loop shown below, what is the vital capacity: 
Select and explain. 
A. 1 liter, B. 5.5 liters, C. 3 liters, D. 4.5 liters
D: 4.5 liters
Answer: D: 4.5 liters 
Explanation: Ans. (d) 4.5 liters(Ref. Guyton and Hall Physiology Review, 3rd ed/p.127)In the graph, residual volume (RV) is 1 LTotal lung capacity (TLC) is 5.5 LVital capacity is TLC-RV=4.5L