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': 'VAS is most widely used to measure \nSelect and explain. \nA. Sleep, B. Sedation, C. Pain intensity, D. Depth of anaesthesia', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The visual analog scale (VAS) is a validated, subjective measure for acute and chronic pain. Scores are recorded by making a handwritten mark on a 10-cm line that represents a continuum between "no pain" and "worst pain."', 'role': 'assistant'}]