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 30 years old male presented with silvery scales on elbow and knee, that bleed on removal. The probable diagnosis is – 
Select and explain. 
A. Pityriasis, B. Seborrhoeic dermatitis, C. Psoriasis, D. Secondary syphilis
C: Psoriasis
Answer: C: Psoriasis 
Explanation: Morphology of papules/plaques in various papulosquamotas disorders

Psoriasis - Erythematous papules and plaques on extensors (elbow & knee
Lichen planus - Violaceous papules with Wickham's striae an flexural surface
Pityriasis rosea - Annular plaques on Trunk
Seborrheic dermatitis - Yellowish, follicular papules on scalp and face 
Pityriasis rubra pilaris - Erythematous follicular papules on Trunk & dorsum of hand
Secondary syphilis - Dusky erythematous papules
Pityriasis lichenoides et varioliformis acuta - Erythematous edematous papules surmounted by vesicles/crust

Coming to question
Clues in this question are :-

Characterstic scales → silver scale
Involvement of elbow & knee
Bleeding on scale removal → Auspitz sign