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': 'Most common cause of solitary thyroid nodule is: \nSelect and explain. \nA. Physiological goiter, B. Follicular adenoma, C. Colloid degenerations, D. Cysts', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]