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
Skin pigmentation is caused by: 
Select and explain. 
A. Methotrexate, B. Dactinomycin, C. Cyclophosphamide, D. Busulphan
D: Busulphan
Answer: D: Busulphan 
Explanation: D i.e. Busulphan