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
Test for β- thalassemia trait - 
Select and explain. 
A. HbA
2, B. HbF, C. Fragility test, D. Coomb's test
A: HbA
2
Answer: A: HbA
2 
Explanation: None