This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
X-bodies called Birbeck granules are characteristically seen in - 
Select and explain. 
A. Granulomatous vasculitis, B. Pulmonary alveolar proteinosis, C. Langerhan's cells granulomatosis, D. Idiopathic pulmonary alveolar proteinosis
C: Langerhan's cells granulomatosis
Answer: C: Langerhan's cells granulomatosis 
Explanation: None