The correct option is:**(d) heparin.**
Explanation:
Heparin prevents blood coagulation in the blood vessels. It is a product of mast cells. It is an anticoagulant, blocking conversion of prothrombin to thrombin. Haemoglobin is the blood pigment necessary for oxygen transport. Plasma is the component of blood. Thrombin is the product of blood clotting.
