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: Anaesthesia
[{'content': 'Which of the following is true to the immediate postoperative period in a young patient with previously normal lungs having upper abdominal surgery ? \nSelect and explain. \nA. Arterial oxygen tension will typically be reduced by an average of 10 mm Hg when breathing room air, B. Arterial oxygen tension will normalize after 15 minutes, C. Diffusion hypoxia is the major determinant of arterial hypoxaemia, D. The CXR will typically reveal no abnormalities', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]