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': 'The Sengstaken tube must maintain a pressure of ... To stop bleeding from varices - \nSelect and explain. \nA. 20 mm Hg, B. 25 mm Hg, C. 35 mm Hg, D. 45 mm Hg', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]