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
certain strains of Streptococcus mutans
a have been proved to be the cause of human dental caries by means of control studies
b depend for their cariogenicity on the production of insoluble polysaccharides
c cause dental caries by the production of lactic and other acids from fermentation of sugar
d are a cause of infective endocarditis
e Will induce smooth surface caries in quotes 
Select and explain. 
A. 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
A: a is false bcde is true
Answer: A: a is false bcde is true 
Explanation: Strep. mutans may be an important organism but not the only one, but controlled studies in humans cannot conceivably be carried out