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
Green stains which occur frequently in children are due to: 
Select and explain. 
A. Enamel deficiency, B. Dentin deficiency, C. Material alba, D. Chromogenic bacteria
D: Chromogenic bacteria
Answer: D: Chromogenic bacteria 
Explanation: None