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': 'A 40 year old female underwent surgery. Postoperatively she told the anaesthetist that she was aware of preoperative events. Individual intraoperative awareness is evaluated by – \nSelect and explain. \nA. Pulse oximetry, B. Colour doppler, C. Bispectral imaging, D. End tidal CO2', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Intraoperative awareness (depth of anaesthesia) is monitored by the Bispectral index.', 'role': 'assistant'}]