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': 'A 85 year old woman with Nikolsky sign-ve, blisters on thigh & trunk, lesions come on & off. What is the cause : \nSelect and explain. \nA. Pemphigus vulgaris, B. Pemphigoid, C. Lichen planus, D. Dermatitis herpetiformis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Pemphigoid', 'role': 'assistant'}]