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': 'Which of the following is a Universal donor? \nSelect and explain. \nA. A Positive, B. O Positive, C. AB Positive, D. O Negative', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]