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': "Nail deformity commonly seen in lichen planus are all of the following except: March 2009 \nSelect and explain. \nA. Pterygium, B. Longitudnal grooves, C. Oncholysis, D. Beau's lines", 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. D: Beau's lines Lichen planus affects one or more nails in 10% of cases, sometimes without involving the skin surface - if all nails are abnormal and nowhere else is affected it is called twenty nail dystrophy. The nail plate tends to thin and may become longitudinally grooved and ridged. The nail may darken, thicken up or lift off the nail bed (onycholysis). Sometimes the cuticle is destroyed and forms a scar (pterygium)-diagnostic. The nails may shed, stop growing altogether and rarely, completely disappear. Beau's lines are transverse grooves that appear simultaneously on all nails", 'role': 'assistant'}]