参考答案：

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`)