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: Medicine
[{'content': 'Carotid body receptors are stimulated when there is: \nSelect and explain. \nA. Increased O2 tension, B. Decreased O2 tension, C. Decreased CO2, D. Increased heart rate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]