This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal System, Subject name: Physiology
[{'content': 'Which of the following is characteristic of saliva? \nSelect and explain. \nA. Hypotonicity relative to plasma, B. A lower HCO3- concentration than plasma, C. The presence of proteases, D. Secretion rate that is increased by vagotomy', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Saliva is characterized by: Hypotonicity High HCO3- concentration (relative to plasma) because of secretion of HCO3- into saliva by the ductal cells. Presence of a-amylase and lingual lipase (not proteases) Because control of saliva production is parasympathetic, it is abolished by vagotomy.', 'role': 'assistant'}]