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: Medicine
Each milliliter of red cells contains ....... mg of elemental iron: 
Select and explain. 
A. 1 mg, B. 2 mg, C. 3 mg, D. 4 mg
A: 1 mg
Answer: A: 1 mg 
Explanation: Each milliliter of red cells contains 1 mg of elemental iron. Reference: Harrisons Principles of Internal Medicine, 18th Edition, Page 845