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': 'Clayton is used in a close breathing system for the purpose of \nSelect and explain. \nA. As a hardner, B. As an absorbent, C. As a softner, D. As an indicator', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D i.e. As an indicator', 'role': 'assistant'}]