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: Surgery
[{'content': "Which is the most common cause of hypothyroidism \nSelect and explain. \nA. Multinodular goiter, B. Lymphoma of thyroid, C. Autoimmune thyroiditis, D. Riedel's thyroiditis", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]