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
[{'content': 'Colonization of a new smooth surface of a tooth will occur by S. mutans when its  level in the oral cavity reaches: \nSelect and explain. \nA. >105/ml, B. 4.5 x 104/ml, C. 3.5 x 103/ml, D. 5.5 x 102/ml', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Levels of S.mutans greater than 105 are indicative of an acceptable cariogenic challenge because\xa0colonization does not occur until the level of S. mutans reaches\xa04.5×104/ml for smooth surface and 103/ml of occlusal ﬁssures.\xa0\nSeveral clinical studies have corroborated the ﬁnding that the percentage\xa0of S.mutans in saliva increases signiﬁcantly as a function of the DMFS score.\xa0\nThere is thus substantial evidence for associating high S.mutans counts with caries activity.\n\nShafers textbook of Oral Pathology – page 468', 'role': 'assistant'}]