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
Major contributor to plasma osmolarity is: 
Select and explain. 
A. Glucose, B. Plasma proteins, C. Urea, D. Sodium
D: Sodium
Answer: D: Sodium 
Explanation: Urea = 2.14 Kh BUN BUN is the Blood Urea Nitrogen