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
A 24 year old man had multiple, small hypopigmented macules on the upper chest and back for the last three months. The macules were circular, arranged around follicles and many had coalesced to form large sheets. The surface of the macules showed fine scaling. e had similar lesions one year ago which subsided with treatment. The most appropriate investigation to confirm the diagnosis is – 
Select and explain. 
A. Potassium hydroxide preparation of scales, B. Slit skin smear from discrete macules, C. Tzanck test, D. Skin biopsy of coalesced macules
A: Potassium hydroxide preparation of scales
Answer: A: Potassium hydroxide preparation of scales 
Explanation: Multiple small hypopigmented macules on chest & back, fine scales, history of perifollicular arrangment and reappearance after treatment suggert the diagnosis of P. versicolor. Examination of scales in 10% KOH shows short hyphae and round spores (sphagetti and meat ball appearance).