The correct option is A Thromoboplastin
Platelets are a source of thromboplastin. Thromboplastin is a plasma protein aiding blood coagulation through catalyzing the conversion of prothrombin to thrombin. It is a complex enzyme that is found in the brain, lung, and other tissues and especially in blood platelets and that functions in the conversion of prothrombin to thrombin in the clotting of blood, called as thrombokinase.