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': 'O2 delivery to tissue is decreased by: \nSelect and explain. \nA. 4,ed Haemoglobin level, B. Ted HCO3, C. Ted Pa CO2, D. All', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. 4-ed Hemoglobin level', 'role': 'assistant'}]