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': 'Eruption of lower 2nd molar occur before lower 2nd premolar; probable reason being \nSelect and explain. \nA. Crowding, B. Impaction of lower 2nd premolar, C. Premature exfoliation of primary 2nd molar, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]