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': 'Nitrous oxide is contraindicated in all except \nSelect and explain. \nA. Vitreo-retinal surgeries, B. Pneumothorax, C. Mastectomy, D. Laser surgery', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Nitrous oxide is contraindicated in\xa0\n\nPneumothorax, pneumoperitoneum\nVitreo-retinal surgery\nCochlear implant surgery\nIntestinal obstruction\nLaser surgery', 'role': 'assistant'}]