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
Under resting conditions, predominant ion in saliva is: 
Select and explain. 
A. Sodium, B. Hydrogen, C. Chloride, D. Bicarbonate
D: Bicarbonate
Answer: D: Bicarbonate 
Explanation: Bicarbonate