This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: parasitology, Subject name: Microbiology
[{'content': 'Cyst phase does not exist in - \nSelect and explain. \nA. Gardenella vaginalis, B. Trichomonas vaginalis, C. Entamoeba hystolytica, D. Entamoeba coli', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Gardnerella is a genus of Gram-variable-staining facultative anaerobic bacteria of which G. vaginalis is the only species. The organisms are small nonspore-forming, nonmotile coccobacilli.', 'role': 'assistant'}]