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': '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: \nSelect and explain. \nA. Chromogenic bacteria, B. Neonatal line, C. Calculus, D. Material alba', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]