This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Psoriasis, Subject name: Skin
Most common site affected by psoriasis is? 
Select and explain. 
A. Flexor surface, B. Extensor surface, C. Palms and soles, D. Oral mucosa
B: Extensor surface
Answer: B: Extensor surface 
Explanation: ANSWER: (B) Extensor surfaceREF: Rook's textbook of dermatology 7th e p. 35.1"Most commonly involved areas in psoriasis is Extensor aspect of knees, elbows & Scalp"