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': 'In serial extraction which is not a contraindication \nSelect and explain. \nA. Impaction of canine, B. Lingual tipping of incisors, C. Ditching, D. Open bite', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]