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 anesthetist that she was aware of preoperative events. Individual intraoperative awareness is evaluated by: \nSelect and explain. \nA. Cerebral pulse oximetry, B. Colour Doppler, C. Bispectral imaging, D. End tidal CO2', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C i.e. Bispectral imaging Intraoperative awareness and depth of anaesthesia can be evaluated by BIS (bispectral index)Q', 'role': 'assistant'}]