The correct answer is D. Calciferol.
Rickets is a softening of the bones in children due to vitamin D deficiency. It can cause the bones to become deformed, especially in the legs. Vitamin D is essential for the absorption of calcium and phosphorus from food. These minerals are necessary for the growth and development of strong bones.
Carotene is a precursor to vitamin A, which is not involved in the development of rickets. Cyanocobalamine is vitamin B12, which is also not involved in the development of rickets. Thiamine is vitamin B1, which is also not involved in the development of rickets.
Rickets is a preventable disease. It can be treated with vitamin D supplements or by exposing the skin to sunlight.