Which of the following enzyme is essential for clotting of blood?

Thrombin is a serine protease, an enzyme, that is at the centre of blood clotting process in human beings. It catalyzes the conversion of fibrinogen to fibrin and activates procoagulant factors V, VIII, XI, and XIII. Additionally, when bound to thrombomodulin, it activates protein C, an anticoagulant zymogen.