This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
[{'content': 'D2O is used to measure \nSelect and explain. \nA. ECE Volume, B. ICF volume, C. TBW volume, D. Plasma volume', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The concentration of the marker in the plasma is measured and from this value, the total body water can be measured. The markers are D2O, tritium oxide, aminopyrine.(Ref: Textbook of medical physiology N Geetha 2nd edition page no.61)', 'role': 'assistant'}]