<prompt> 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 ?Alveolar hypoventilationPrimary pulmonary hypeensionInterstitial lung diseaseAnxiety  <response>: In primary pulmonary hypeension: Pulmonary function tests shows Non restrictive Non obstructive FVC,FEV1,FEV1FVC Are normal where as DLCO is characteristically decreased 