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: Pathology
At birth mouth is sterile,first bacteria to appear in oral cavity: 
Select and explain. 
A. Streptococcus salivarius., B. Streptococcus mutans., C. Streptococcus sanguis., D. Streptococcus mitis.
A: Streptococcus salivarius.
Answer: A: Streptococcus salivarius. 
Explanation: None