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: Dental
The concentration of constituents in saliva depends on: 
Select and explain. 
A. Nature of stimulus., B. Duration of the stimulus., C. Rate of flow., D. Differential gland contribution.
C: Rate of flow.
Answer: C: Rate of flow. 
Explanation: Other important factors affecting the composition of saliva are flow rate, differential gland contribution, circadian rhythm, duration of stimulus, nature of stimulus and diet.
The concentration of constituents in saliva depends only on the rate of flow and not on the nature of stimulus.