This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Physiology
[{'content': 'What is the expected mixed venous oxygen tension, in mm Hg, in a normal adult after breathing 100% oxygen for 10 minutes? \nSelect and explain. \nA. 150, B. 740, C. 45, D. 573', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. (c) 45Ref: American Board of Anesthesiology American Society of Anesthesiologists, Book A 1996 q-67Breathing 100% oxygen will not change the oxygen saturation much. In arterial blood it is around 97% saturation which corresponds to a PO2 of 100 mm HgIn venous blood it is 75% saturation which corresponds to a mixed venous oxygen tension of around 40-45 mm Hg', 'role': 'assistant'}]