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: Unknown
[{'content': 'Partial pressure of CO2 is lowest in: \nSelect and explain. \nA. Arterial blood, B. End tidal air, C. Expired air, D. Venous blood', 'role': 'user'}, {'content': 'Answer: C \nExplanation: (Refer: Ganong Figure 34-15, 24th edition, pg no: 635)\nNormal P02 and PC02 at various sites', 'role': 'assistant'}]