The correct option is C Vitamin K
A. Vitamin A takes part in the formation of visual retinal pigments like rhodopsin, iodopsin etc. and thus, it is required for normal vision.
B. Vitamin D regulates the metabolism of calcium and phosphorus and in turn affects the growth of body by affecting the growth of bone and teeth.
C. Vitamin E is necessary for maintaining sterility.
D. Vitamin K is necessary for the formation of prothrombin (important component of blood clotting mechanism) in the liver of human beings and thus, it is involved in clotting of blood.
So, the correct answer is Vitamin K.