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: Physiology
[{'content': 'During exercise, increase in O2 delivery to muscles is because of all except \nSelect and explain. \nA. Oxygen dissociation curve shifts to left, B. Increased stroke volume, C. Increased extraction of oxygen from the blood, D. Increased blood flow to muscles', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Hb-O2 dissociation curve shift to left indicates more affinity of Hb to O2 and thus less delivery of O2 to tissues. Exercise causes increased 2,3 DPG.\nShift to left seen in\n-\xa0\xa0\xa0\xa0\xa0\xa0\xa0 Increased pH\n-\xa0\xa0\xa0\xa0\xa0\xa0\xa0 Decreased 2,3 DPG, temperature, PCO2\n-\xa0\xa0\xa0\xa0\xa0\xa0\xa0 HbF (Fetal)\nShift to right seen in\n-\xa0\xa0\xa0\xa0\xa0\xa0\xa0 Decreased pH\n-\xa0\xa0\xa0\xa0\xa0\xa0\xa0 Increased 2,3DPG, temperature, PCO2\n-\xa0\xa0\xa0\xa0\xa0\xa0\xa0 HbS (Sickle cell)', 'role': 'assistant'}]