This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chronic Venous Insufficiency, Subject name: Surgery
[{'content': 'Deep vein thrombosis is seen in all except one: \nSelect and explain. \nA. Prolonged immobilization, B. Subungual melanoma, C. Pregnancy, D. Major surgical operation.', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' ie Subungual melanoma Risk factors for venous thromboembolism Patient FactorsDisease or surgical procedureAgeTrauma or surgery, especially of pelvis, hip, lower limbObesityMalignancy, especially pelvic, abdominal metastaticVaricose veins /superficial thrombophlebitisHeart failureImmobilityRecent myocardial infractionPregnancyParalysis of lower limb(s)PuerperiumInfectionHigh-dose oestrogen therapyInflammatory bowel diseasePrevious deep vein thrombosis or pulmonary embolismNephrotic syndromeThrombophiliaPolycythaemicaDeficiency of anti-thrombin III, protein C or protein SParaproteinemiaAnti-phospholipidParoxysmal nocturnal hemoglobinuria antibody or lupus anticoagulant Behcet's disease Homocystinemia", 'role': 'assistant'}]