This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Concepts in physiology, Subject name: Physiology
[{'content': 'Major contributor to plasma osmolarity is: \nSelect and explain. \nA. Glucose, B. Plasma proteins, C. Urea, D. Sodium', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Urea = 2.14 Kh BUN BUN is the Blood Urea Nitrogen', 'role': 'assistant'}]