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': "Incision of which fibres of PDL doesn't increase mobility of tooth: \nSelect and explain. \nA. Oblique fibres, B. Alveolar crest fibres, C. Apical fibres, D. Transeptal fibres.", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]