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: Skin
[{'content': "All are true about Langerhans' histocytosis except? \nSelect and explain. \nA. Common before 3 years of age, B. Letterer Siwe disease is systemic manifestation, C. Radio sensitive, D. Testis is commonly involved", 'role': 'user'}, {'content': 'Answer: D \nExplanation: D. i.e. Testis is commonly invoved', 'role': 'assistant'}]