This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Physiology
[{'content': 'A child has been brought with the following scalp lesion with history of itching in scalp and hair loss for past 2 months. Which of the following is useful for diagnosis of this patient? \nSelect and explain. \nA. Gram stain, B. KOH mount, C. Slit Skin smear, D. Tzanck smear', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. B KOH mountRef: Fitzpatrick's Dermatology, 8th ed. pg. 2284-85The image shows black dot sign classical of tinea capitis. The hairs are damaged due to endothrix infection and break easily.", 'role': 'assistant'}]