This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
Nitrates in excess of ----mg/L may cause infantile methaemoglobinemia 
Select and explain. 
A. 15, B. 25, C. 35, D. 45
D: 45
Answer: D: 45 
Explanation: Nitrates level >50 increases the risk of infantile methaemoglobinaemia. Ref: Park's textbook of PSM 25th edition, pg 783