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 common cause for gingival fistula in children is: \nSelect and explain. \nA. Acute apical abscess, B. Acute periodontal abscess, C. Periapical cyst, D. Chronic apical lesion', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]