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: Physiology
[{'content': 'Fluid content of the blood is: \nSelect and explain. \nA. Plasma, B. Serum, C. Water, D. Tissue fluid', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]