Ans. C. Idiopathic Pulmonary Fibrosis.a. This patient has a reduced FEV1 and FVC with a preserved FEV1/FVC ratio.b. The total lung capacity is reduced and the patient, therefore, has a restrictive defect.c. The flow-volume loop also has the characteristic appearance of a restrictive process - tall, narrow and a short expiratory phase.d. Based on the fact that his TLC is below 50% predicted, this would be classified as a "severe" restrictive defect.e. His DLCO is also markedly reduced indicating he has a reduced alveolocapillary interface for gas exchange and suggesting that the cause of his restrictive process lies within the lung parenchyma.f. Idiopathic pulmonary fibrosis might be a cause in this case.