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
A 60-years old male has been operated for carcinoma of caecum and right hemicolectomy has been done. On the fouh post - oprative day, the patient develops fever and pain in the legs.The most impoant clinical entity one should look for is - 
Select and explain. 
A. Urinary tract infection, B. Intravenous line infection, C. Chest infection, D. Deep vein thrombosis
D: Deep vein thrombosis
Answer: D: Deep vein thrombosis 
Explanation: Ans. is `d' i.e., Deep vein thrombosis Old age and post operative period are risk factor for deep vein thrombosis