This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pharmacology
A 85 year old female developed multiple blisters on trunk and thighs. Nikolsky's sign negative. The lesions came on and off. The most probable diagnosis is NOT RELATED-DERMATOLOGY 
Select and explain. 
A. Pemphigus vulgaris, B. Bullous pemphigoid, C. Lichen planus, D. Lepra reaction
B: Bullous pemphigoid
Answer: B: Bullous pemphigoid 
Explanation: .