This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Preoperative assessment and monitoring in anaesthesia, Subject name: Anaesthesia
[{'content': 'Modern monitors to measure ETCO2 make Use of- \nSelect and explain. \nA. Infrared absorption spectroscopy, B. Ultra violet rays, C. Laser technology, D. Scatter technology', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Capnograpghy works on the priniciple of absorption spectrophotometry(CO2 absorbs infrared rays at a wavelength of 4280 nm)', 'role': 'assistant'}]