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: Pediatrics
[{'content': 'Most common cause of thyrotoxicosis in childhood ? \nSelect and explain. \nA. Toxic nodular goitre, B. Toxic adenoma, C. Graves disease, D. Thryotoxicosis factitia', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]