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
All of the following skin lesions are  premalignant except 
Select and explain. 
A. Actinic keratosis, B. Oral leucoplakia, C. Bowen's disease, D. Acanthosis nigricans
D: Acanthosis nigricans
Answer: D: Acanthosis nigricans 
Explanation: Acanthosis nigricans is a skin lesion seen with underlying gastric malignancy, but it is not a precancerous lesion.