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
Best denotes airway resistance 
Select and explain. 
A. Vital Capacity, B. Mid respiratory flow rates, C. FEV1, D. Total volume
B: Mid respiratory flow rates
Answer: B: Mid respiratory flow rates 
Explanation: The maximal expiratory flow at 50 % of the forced vital capacity (MEF50) is the flow where half of forced vital capacity (FVC) remains to be exhaled . It corresponds to the forced expiratory flow at 50 % (FEF50) and correlates highly with the maximum mid-expiratory flow (FEF25-75 %) Ref: guyton and hall textbook of medical physiology 12 edition page number:326,327,328