Which of the Following Correctly Describes the Structure of Normal $\alpha$

Which of the following correctly describes the structure of normal hemoglobin A (Hb A) ?

A) four identical polypeptide chains, each containing two heme groups
B) two $\alpha$ and two $\beta$ polypeptide chains, each containing one heme group
C) conjugated protein with 141 amino acids, containing two atoms of iron
D) two $\delta$ and two $\gamma$ polypeptide chains, each containing a single heme group