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. Decreased haemoglobin level, B. Increased haemoglobin level, C. Increased PaCO2, D. Increased HCO3', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]