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: Pathology
Pigmentation occurs in oral cavity and skin in all of the
following except: 
Select and explain. 
A. Peutz-jeghers syndrome, B. Addison's syndrome, C. Cushing syndrome, D. Albright syndrome
C: Cushing syndrome
Answer: C: Cushing syndrome 
Explanation: None