This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Psoriasis, Subject name: Dental
The commonest sign of nail psoriasis is: 
Select and explain. 
A. Pitting, B. Pterygium, C. Oil drop sign, D. Onycholysis
A: Pitting
Answer: A: Pitting 
Explanation: Nail changes in psoriasis - Most common - Nail pitting/Thimble pitting Most characteristic - oil drop sign/ salmon patch Onycholysis Leukonychia Subungual hyperkeratosis Nail tunnel