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
The test likely to help in diagnosis of a patient who presents with an itchy annular plaque on the face is – 
Select and explain. 
A. Gram's stain, B. Potassium hydroxide mount, C. Tissue smear, D. Wood's lamp examination
B: Potassium hydroxide mount
Answer: B: Potassium hydroxide mount 
Explanation: The clinical picture is suggestive of a fungal infection most likely Tinea fascitis, KOH preparation is performed on scaling skin lesion when fungal etiology is suspected. Microscope examination after KOH digestion will show fungal hyphae.