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': 'Under resting conditions, predominant ion in saliva is: \nSelect and explain. \nA. Sodium, B. Hydrogen, C. Chloride, D. Bicarbonate', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Bicarbonate', 'role': 'assistant'}]