In order to produce a massive amount of fibrin molecules, thrombin needs to be present. To ensure abundance of thrombin production, thrombin stimulates its own production by stimulating the formation of tissue factor and PF-3, which activates further platelet aggregation. This pattern of stimulation is known as a

Positive feedback loop

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.