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: Microbiology
Human immunoglobulins are divided based on 
Select and explain. 
A. Functional differences, B. Structural differences, C. Complement fixation, D. None of the above
B: Structural differences
Answer: B: Structural differences 
Explanation: None