You are answering a USMLE-style medical question. Question: A 35-year-old Caucasian female presents to the emergency room with unilateral leg swelling. She reports that she developed painful left-sided leg swelling and redness earlier in the day. She is otherwise healthy and takes no medications. She denies any recent prolonged travel. She experienced a similar episode affecting the opposite leg one year ago and was diagnosed with a thrombus in the right femoral vein. On examination, the left leg is erythematous and swollen. Passive dorsiflexion of the left ankle elicits pain in the left calf. Ultrasound of the leg reveals a thrombus in the left popliteal vein. A genetic workup reveals that she has an inherited condition. What is the most likely pathophysiology of this patient’s condition? Options: A) Elevated serum homocysteine B) Thrombin inhibitor deficiency C) Auto-antibodies directed against phospholipids D) Resistance to clotting factor degradation Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.