Explanation:
Prothrombin is made by vitamin K, which is a fat-soluble vitamin absorbed by the small intestine. Vitamin K is a fat-soluble vitamin, which is needed by humans to synthesize certain types of proteins. Vitamin K deficiency causes blood to not clot. Prothrombin is a protein made by the liver. Prothrombin helps blood to clot. Hence, the correct option is (B).