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: Surgery
[{'content': 'It is difficult to obtain local infiltration anesthesia in the presence of inflammation because of \nSelect and explain. \nA. a decreased PH, B. increased vascularity, C. oedema, D. pain', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]