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': 'Variation of eruption of secondary dentition can be: \nSelect and explain. \nA. 4-5 months., B. 6-7 months., C. 12-18 month., D. Variations in eruption of secondary dentition is less frequent.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]