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
Mother of a child is worried about green stains on the recently erupted upper anterior teeth of her child. The stains are most probably due to: 
Select and explain. 
A. Chromogenic bacteria, B. Neonatal line, C. Calculus, D. Material alba
A: Chromogenic bacteria
Answer: A: Chromogenic bacteria 
Explanation: None