The following are multiple choice questions (with answers) about medical knowledge.   **Question:** Main mechanism of action of heparin Is to prevent:   (A) Conversion of fibrinogen to fibrin   (B) Conversion of prothrombin to thrombin   (C) PTC to PTA   (D) Factor VIIa inhibition
['(B) Conversion of prothrombin to thrombin <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) Conversion of fibrinogen to fibrin \n (B) Conversion of prothrombin to thrombin \n (C) PTC to PTA \n (D) Factor VIIa inhibition <> possible answers', '  Main mechanism of action of heparin Is to prevent: <> context@']