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: Radiology
[{'content': 'Most sensitive investigation for air embolism is \nSelect and explain. \nA. Decreased tidal volume of CO2, B. Decreased tidal volume of NO2, C. Doppler ultrasound, D. Central Venous Presure', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C i.e. Doppler Ultrasound', 'role': 'assistant'}]