Answer:
Positive feedback loop
Step-by-step explanation:
Thrombin is a protease which is involved in the physiological role of blood clotting and homeostasis. A Blood clot is formed when a mesh-like structure is formed with the fibrin molecules.
The formation of fibrin molecules requires thrombin proteases which converts the fibrinogen to fibrin molecules. To produce more fibrin molecules, thrombin is required in higher amount.
To produce a high amount of thrombin, thrombin stimulates its production. Such physiological loop where the production of the product proceeds reaction in the forward direction and stimulates its production is known as a positive feedback loop.
Thus, a positive feedback loop is the correct answer.