【正确答案】Concept: The coagulation system consists of cofactors and a series of zymogens which sequentially activate one another, leading to formation of fibrin at a site of vascular injury. (3`) Basic steps should be as follows: (1) First Step: activator of prothrombin (4`) (2) Second Step: prothrombin thrombin (4`) (3) Third Step: fibrinogen fibrin (4`)