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': 'This law of plethysmography explains principle of working in \nSelect and explain. \nA. Capnography, B. Oximetry, C. CVP monitor, D. Entropy', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The\xa0 law of plethysmography explains working of pulse oximeter.', 'role': 'assistant'}]