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
Which among the following is the most common site affected by psoriasis? 
Select and explain. 
A. Flexor surface, B. Extensor surface, C. Palms and soles, D. Oral mucosa
B: Extensor surface
Answer: B: Extensor surface 
Explanation: In psoriasis, classically patients develop sharply demarcated red plaques (raised plateaulike lesions) with silvery white scale distributed about the scalp, trunk, and limbs, with a predilection for extensor surfaces such as the elbows and knees.