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': 'True about body fluid osmolarity ? \nSelect and explain. \nA. Major contributor is proteins, B. Major contributor is Na+, C. ECF osmolarity is 250 mOsm/L, D. Measured by dilution method', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Major contributor is Na+", 'role': 'assistant'}]