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: Social & Preventive Medicine
A child is exclusively fed on cow's milk, the deficiency seen in: 
Select and explain. 
A. Iron, B. Riboflavin, C. Vitamin-A, D. Thiamine
A: Iron
Answer: A: Iron 
Explanation: Iron