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
Earliest sign of deep vein thrombosis is 
Select and explain. 
A. Calf tenderness, B. Rise in temperature, C. Swelling of calf muscle, D. Homan's sign
A: Calf tenderness
Answer: A: Calf tenderness 
Explanation: None