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: Microbiology
Bacterial species which is protective or beneficial to the host is 
Select and explain. 
A. Streptococcus sanguis, B. Porphyromonas gingivalis, C. Treponema denticola, D. Spirochetes
A: Streptococcus sanguis
Answer: A: Streptococcus sanguis 
Explanation: None