This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
Causes of Hypocalcemia in a child are- 
Select and explain. 
A. DiGeorge syndrome, B. Hypoparathyroidism, C. Magnesium deficiency, D. All of above
D: All of above
Answer: D: All of above 
Explanation: Causes of hypocalcemia 

Hypoparathyroidism
DiGeorge syndrome
PTH receptor defect (pseudohypoparathyroidism)
Magnesium deficiency
Exogenous organic phosphate excess
Vit D difecideciency