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: Gynaecology & Obstetrics
Dietary supplement alone can not compensate for the increased requirement of which nutrient in pregnant women : 
Select and explain. 
A. Iron, B. Iodine, C. Magnesium, D. Calcium
A: Iron
Answer: A: Iron 
Explanation: Iron