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: Surgery
Deep vein thrombosis is seen in all except one - 
Select and explain. 
A. Prolonged immobilization, B. Subungual melanoma, C. Pregnancy, D. Major surgical operation.
B: Subungual melanoma
Answer: B: Subungual melanoma 
Explanation: None