This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid & Electrolyte, Subject name: Medicine
[{'content': 'Which one of the following is the major determinant of plasma osmolality - \nSelect and explain. \nA. Serum sodium, B. Serum potassium, C. Blood glucose, D. Blood urea nitrogen', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Serum sodium o Plasma osmolality = 2 (sodium + potassium)+BUN2.8+Blood sugar18", 'role': 'assistant'}]