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: Medicine
A patient is admitted with 3rd episode of deep venous thrombosis. There is no history of any associated medical illness. All of the following investigations are required for establishing the diagnosis except- 
Select and explain. 
A. Proteing C deficiency, B. Antithrombin III deficiency, C. Antibodies to factor VIII, D. Antibodies to cardiolipin
C: Antibodies to factor VIII
Answer: C: Antibodies to factor VIII 
Explanation: None