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
Adult haemoglobin consists of which one of the following tetramer of chains ? 
Select and explain. 
A. 2α+ 2β, B. 2α+ 2δ, C. 2β + 2γ, D. 2α + 2γ
A: 2α+ 2β
Answer: A: 2α+ 2β 
Explanation: None