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: Dental
[{'content': 'Pitting of nails is seen in – a) Lichen planusb) Psoriasisc) Pemphigusd) Arsenic poisoning \nSelect and explain. \nA. ab, B. a, C. ad, D. bc', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]