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: Pathology
A lady in the second trimester underwent a hemogram and her hemoglobin was found to be 6mg%. The gynaecologist suggested for IV transfusion of packed red cells to improve the level.

How much of iron is absorbed by transfusion of 2 units of packed red cells? 
Select and explain. 
A. 2gm, B. 2mg, C. 1gm, D. 500mg
D: 500mg
Answer: D: 500mg 
Explanation: None