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
In an asthmatic patient which of the following pulmonary functions would show the greater improvement on inhaling a bronchodilator 
Select and explain. 
A. Tidal volume, B. FEV1, C. FEF 25deg-75%, D. FVC
B: FEV1
Answer: B: FEV1 
Explanation: In an asthmatic patient,simple spirometry confirms airflow limitation with a reduced FEV1,FEV1/FVC ratio,and PEF(peak ejection fraction).Reversibility is demonstrated by a>12% and (200 ml) increase in FEV1 15 minutes after an inhaled sho acting beta2 agonist(bronchodilator).In some patients,similar response is obtained by a 2 to 4 week trial of oral coicisteroids(prednisolone30-40 mg daily). Reference;:Harrison's Medicine,18the edition,page no:2109.