<prompt> A 60-years old male has been operated for carcinoma of caecum and right hemicolectomy has been done. On the fourth post - oprative day, the patient develops fever and pain in the legs.The most important clinical entity one should look for is -Urinary tract infectionIntravenous line infectionChest infectionDeep vein thrombosis  <response>: Old age and post operative period are risk factor for deep vein thrombosis. 