This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Physiology
Which of the following is the best for measuring total body water: 
Select and explain. 
A. Evan's blue, B. I131, C. Tritium oxide, D. P 32
C: Tritium oxide
Answer: C: Tritium oxide 
Explanation: Ans. C. Tritium oxideRadioactive water (TRITIUM) or heavy water (deuterium) can be used to measure total body water. Tritium is also used as a tracer in chemical and biochemical research.