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: Dental
[{'content': 'A white soft sticky deposit on tooth surface \nSelect and explain. \nA. Materia alba, B. Linea alba, C. Plaque, D. Calculus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]