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': 'Phoenix abscess is \nSelect and explain. \nA. Reversible pulpits., B. Acute apical periodontitis, C. Acute exacerbation of an existing chronic inflammation, D. Chronic abscess', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]