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': 'A 29 yr old unmarried female presents with dyspnea. Her chest X-ray is normal, FVC is 92%, FEV1/ FVC is 89% and DLCO is 59% of normal. On exercise her oxygen saturation drops from 92% to 86%. What is the likely diagnosis ? \nSelect and explain. \nA. Alveolar hypoventilation, B. Primary pulmonary hypeension, C. Interstitial lung disease, D. Anxiety', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In primary pulmonary hypeension: Pulmonary function tests shows Non restrictive Non obstructive FVC,FEV1,FEV1/FVC Are normal where as DLCO is characteristically decreased', 'role': 'assistant'}]