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': 'Skin pigmentation is caused by: \nSelect and explain. \nA. Methotrexate, B. Dactinomycin, C. Cyclophosphamide, D. Busulphan', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D i.e. Busulphan', 'role': 'assistant'}]