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
8 year old boy presented with boggy swelling on the scalp and easily pluckable hair. which of the following is the investigation of choice? 
Select and explain. 
A. Biopsy, B. X ray skull, C. KOH smear, D. Tzank smear
C: KOH smear
Answer: C: KOH smear 
Explanation: The diagnosis is tinea capitis hence investigation of choice is KOH smear.