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
Clayton is used in a close breathing system for the purpose of – 
Select and explain. 
A. As a hardner, B. As an absorbent, C. As a softner, D. As an indicator
D: As an indicator
Answer: D: As an indicator 
Explanation: Clayton is used as an indicator. It is red when sodalime is fresh and becomes yellow when sodalime is exhausted.