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
[{'content': 'Bacterial species which is protective or beneficial to the host is \nSelect and explain. \nA. Streptococcus sanguis, B. Porphyromonas gingivalis, C. Treponema denticola, D. Spirochetes', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]