This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pneumonia, Bronchiectasis, and Lung Abscess, Subject name: Medicine
Most common cause of idiopathic interstitial pneumonia is- 
Select and explain. 
A. Sarcoidosis, B. Organizing pneumonia, C. Idiopathic pulmonary fibrosis, D. Lipoid pneumonia
C: Idiopathic pulmonary fibrosis
Answer: C: Idiopathic pulmonary fibrosis 
Explanation: Ans. is 'c' i.e., Idiopathic pulmonary fibrosis Diffuse parenchymal lung disease | | | | |DPLD of known cause eg, drugs or association eg, rheumatic diseaseIdiopathic interstitial pneumonia (lIPs)Granulomatous DPLD eg, sarcoidosisOther forms of DPLD eg, LAM, PLCH, etc | Non-familial(>80 percent)Familial(2 to 20 percent) | | | | ChronicfibrosingAcute/subacutefibrosingSmokingrelated|||o Idiopatic pulmonary fibrosiso Idiopathic nonspecific interstitial pneumoniao Cryptogenic organizing pneumoniao Acute interstitial pneumoniao Respiratory bronchiolitis interstitial lung diseaseo Desquamative interstitial pneumonia o Diffuse parenchymal lung diseases consist of disorders of known causes (rheumatic disease, environmental or drug related) as well as disorders of unknown cause.o The latter include idiopathic interstitial pneumonias, granulomatous lung disorders (eg, sarcoidosis), and other forms of interstitial lung disease including lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis/ histiocytosis X, and eosinophilic pneumonia.o The interstitial pneumonias are further categorized as chronic fibrosing, acute or subacute fibrosing, or smoking related.o Lymphocytic interstitial pneumonia is typically associated with other disease processes, such as rheumatic disease or immunosuppression; idiopathic lymphocytic pneumonia is rare.o DPLD: diffuse parenchymal lung disease; IIP: idiopathic interstitial pneumonia; LAM: lymphangioleiomyomatosis; PLCH: pulmonary Langerhans cell histiocytosis/histiocytosis X.