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
Organisms involved in smooth surface caries: 
Select and explain. 
A. Streptococcus mutans., B. Lactobacillus., C. Actinomyces., D. All of the above.
A: Streptococcus mutans.
Answer: A: Streptococcus mutans. 
Explanation: None