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: Pharmacology
[{'content': 'Nitrous oxide is carried in the blood stream by \nSelect and explain. \nA. Haemoglobin, B. White blood cells, C. Red Blood cells, D. Serum', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]