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
Characteristic nail finding in lichen planus is 
Select and explain. 
A. Pterygium, B. Hyperpigmentation of nails, C. Pitting, D. Beau's lines
A: Pterygium
Answer: A: Pterygium 
Explanation: Pterygium formation is the characteristic nail finding in lichen planus of nails iadvl textbook of dermatology page 800