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: Physiology
[{'content': 'The vitamin K dependent protein C and S are characterised by their ability to inactivate factor: \nSelect and explain. \nA. 8a and 5a, B. 7a and 5b, C. 3a and 3b, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Sequence of Events Involved in the Activation of Plasminogen\n\nDuring intravascular clotting, the endothelium of the blood vessel secretes a thrombin-binding protein, the thrombomodulin. It is secreted by the endothelium of all the blood vessels, except the minute vessels of brain.\nThrombomodulin combines with thrombin and forms a thrombomodulin-thrombin complex.\nThrombomodulin-thrombin\xa0 complex\xa0 activates protein C.\nActivated protein C inactivates factor V and VIII in the presence of a cofactor called protein S.\nProtein C also inactivates the t-PA inhibitor.\nNow, the t-PA becomes active.\nActivated\xa0t-PA\xa0and\xa0lysosomal\xa0enzymes\xa0activate plasminogen to form plasmin. Plasminogen is also activated by thrombin and u-PA.', 'role': 'assistant'}]