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: Dental
[{'content': 'How many days took to form 1mm layer of enamel: \nSelect and explain. \nA. 90 days., B. 140 days., C. 240 days., D. 180 days.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Mean of daily rate of enamel formation – 3.5µm/day to 4µm/day\nSo to form 1mm thickness total approximately 240 days needed.', 'role': 'assistant'}]