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: Skin
[{'content': "Characterstic nail finding in lichen planus \nSelect and explain. \nA. Pitting, B. Pterygium, C. Beau's Lines, D. Hyperpigmentation of nails", 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Pterygium', 'role': 'assistant'}]