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
Which of the following may result in sudden increase in ETCO2– 
Select and explain. 
A. Malignant hyperthermia, B. Hyperthyrodism, C. Shivering, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Malignant hyperthermia, hypermetabolic states (hyperthyroidism) and increased skeletal muscle activity (shivering) can cause rise in ETCO2