Answer: A. Prothrombin is converted into thrombin which acts on fibrinogen.
Explanation:
Prothrombin is a protein which is converted into thrombin through a blood clotting factor that is known as factor X or prothrombinase.
Thrombin then transform the fibrinogen protein into fibrin threads. The fibrin thread acts like a wire mesh to trap the blood cells and forms a scab or clot. This entire process is called as coagulation.
