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
Which of the following being is the most frequent site of thrombus? 
Select and explain. 
A. Veins of lower extremities, B. Portal vein, C. Pulmonary vein, D. Hepatic vein
A: Veins of lower extremities
Answer: A: Veins of lower extremities 
Explanation: None