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: Social & Preventive Medicine
[{'content': 'The composition of ORS recommended by WHO is \nSelect and explain. \nA. 3.5 g NaCl, B. 4.5 g NaCl, C. 2.9 g sodium-potassium citrate, D. 2.8 g sodium bicarbonate', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]