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
[{'content': 'certain strains of Streptococcus mutans\na have been proved to be the cause of human dental caries by means of control studies\nb depend for their cariogenicity on the production of insoluble polysaccharides\nc cause dental caries by the production of lactic and other acids from fermentation of sugar\nd are a cause of infective endocarditis\ne Will induce smooth surface caries in quotes \nSelect and explain. \nA. a is false bcde is true, B. a b is false c d e is true, C. a b c is false d e is true, D. abcd is false e is true', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Strep. mutans may be an important organism but not the only one, but controlled studies in humans cannot conceivably be carried out', 'role': 'assistant'}]