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': 'The most abundant principal fibre group in periodontal ligament is: \nSelect and explain. \nA. Horizontal, B. Transeptal, C. Apical, D. Oblique', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]