This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pathology
The four "Pyrole rings" in hemoglobin molecule are joined together by 
Select and explain. 
A. Disulphide bridges, B. Methylene bridges, C. Hydrogen bonds, D. Alpha bonds
B: Methylene bridges
Answer: B: Methylene bridges 
Explanation: .