Which of the following is true regarding the effectors of hemoglobin-oxygen binding?

A)an increase in blood pH will cause hemoglobin to bind more tightly to oxygen
B)increased CO₂ from increased muscle activity will result in an increase in the R state of hemoglobin
C)increased Cl^- will cause the formation of a salt bridge between two Lys residues,one on an $\alpha$ subunit,the other on a $\beta$ subunit
D)the binding site of 2,3-BPG contains several Asp and Glu residues which are repelled by the similar charge,pushing the two $\beta$ subunits away from each other
E)all of the above