Explanation

Blood clotting factors are released from platelets (thrombocytes). When a blood vessel is injured, platelets aggregate at the site and release thromboplastin and other clotting factors that trigger the coagulation cascade, converting fibrinogen to fibrin. RBCs carry oxygen, eosinophils fight parasites, and monocytes are phagocytic immune cells; none release clotting factors. The answer is (C).