This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Autoimmune skin disorders, Subject name: Dental
[{'content': "Characteristic nail finding in lichen planus is \nSelect and explain. \nA. Pterygium, B. Hyperpigmentation of nails, C. Pitting, D. Beau's lines", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Pterygium formation is the characteristic nail finding in lichen planus of nails iadvl textbook of dermatology page 800', 'role': 'assistant'}]