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': 'Linea alba is \nSelect and explain. \nA. A type of frictional hyperkeratosis that appears as a linear white line in buccal mucosa., B. Usually present as ulcers, C. Traumatic implantation of amalgam particles into mucosa., D. Caused by a chemical in tobacco smoke that stimulates melanin production.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]