Concept:Vitamin D deficiency causes a bone-softening disease in children.Explanation:Vitamin D helps the body absorb calcium and phosphorus, which are essential for strong bones.When there is a deficiency, bones become weak and deformed, resulting in rickets.The other options are caused by different vitamin deficiencies: beriberi (vitamin B1), pellagra (niacin), and scurvy (vitamin C).Answer:C. ricket