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': 'The hyperosmolarity of the renal meduila is due to increased content of - \nSelect and explain. \nA. K+, B. Na +, C. Glucose, D. Na ++', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Na +', 'role': 'assistant'}]