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: Medicine
[{'content': 'For the diagnosis of obstructive airway disease which of the following is preferred \nSelect and explain. \nA. Vital capacity, B. Timed vital capacity, C. Tidal volume, D. Blood gas analysis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In obstructive airway diseases fev1 is markedly reduced than FVC. Maximum mid expiratory flow rate(fev 25 -75 %) is the more sensitive measure of small airway obstruction.', 'role': 'assistant'}]